Radiopaque intraluminal stents comprising cobalt-based alloys with primarily single-phase supersaturated tungsten content

ABSTRACT

Embodiments are directed to radiopaque implantable structures (e.g., stents) formed of cobalt-based alloys that comprise cobalt, chromium, tungsten, and nickel. Tungsten is present above its solubility limit (about 15%), but is still only present as a super-saturated, primarily single-phase material exhibiting an FCC microcrystalline structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation in part of U.S. patentapplication Ser. No. 15/429,339, filed Feb. 10, 2017, now U.S. Pat. No.10,441,445, which is a divisional of U.S. patent application Ser. No.13/830,404, filed Mar. 14, 2013, now U.S. Pat. No. 9,566,147, which is acontinuation in part of U.S. patent application Ser. No. 13/298,070,filed Nov. 16, 2011, now abandoned, which claims the benefit of U.S.Provisional Patent Application Ser. No. 61/414,566 filed Nov. 17, 2010and entitled RADIOPAQUE INTRALUMINAL STENTS COMPRISING COBALT-BASEDALLOYS CONTAINING ONE OR MORE PLATINUM GROUP METALS, each of which isherein incorporated by reference in its entirety.

BACKGROUND

Intraluminal stents implanted with percutaneous methods have become astandard adjunct to procedures such as balloon angioplasty in thetreatment of atherosclerotic disease of the arterial system. Stents, bypreventing acute vessel recoil, improve long term patient outcome andhave other benefits such as securing vessel dissections.

Intraluminal stents comprise generally tubular-shaped devices which areconstructed to hold open a segment of a blood vessel or other anatomicallumen. Intraluminal stents are used in treatment of diseases such asatherosclerotic stenosis as well as diseases of the stomach andesophagus, and for urinary tract applications. Adequate stent functionrequires a precise placement of the stent over a lesion or site ofplaque or other lumen site in need of treatment. Typically, the stent isdelivered to a treatment site by a delivery catheter that comprises anexpandable portion for expanding the stent within the lumen.

The delivery catheter onto which the stent is mounted may be a balloondelivery catheter similar to those used for balloon angioplastyprocedures. In order for the stent to remain in place on the balloonduring delivery to the site of damage within a lumen, the stent may becompressed onto the balloon. The catheter and stent assembly isintroduced within a patient's vasculature using a guide wire. The guidewire is disposed across the damaged arterial section and then thecatheter-stent assembly is advanced over the guide wire within theartery until the stent is directly within the lesion or the damagedsection.

The balloon of the catheter is expanded, expanding the stent against theartery wall. The artery is preferably slightly expanded by the expansionof the stent to seat or otherwise fix the stent to prevent movement. Insome circumstances during treatment of stenotic portions of the artery,the artery may have to be expanded considerably in order to facilitatepassage of blood or other fluid therethrough. In the case of a selfexpanding stent, the stent is expanded by retraction of a sheath oractuation of a release mechanism. Self-expanding stents may expand tothe vessel wall automatically without the aid of a dilation balloon,although such a dilation balloon may be used for another purpose.

These manipulations are performed within the body of a patient by apractitioner who may rely upon both placement markers on the stentcatheter and on the radiopacity of the stent itself. The stentradiopacity arises from a combination of stent material and stentpattern, including stent strut or wall thickness. After deploymentwithin the vessel, the stent radiopacity should allow adequatevisibility of both the stent and the underlying vessel and/or lesionmorphology under fluoroscopic visualization.

Embodiments of the present disclosure are directed to radiopaque cobaltalloys, radiopaque implantable structures (e.g., stents) and relatedmethods of manufacture and use. One embodiment of the present inventionincludes a radiopaque implantable structure. The radiopaque implantablestructure comprises a main body including a cobalt-based alloy thatincludes cobalt, chromium, and one or more radiopaque elements. In oneembodiment, examples of radiopaque elements include so-called platinumgroup metals (i.e., platinum, palladium, ruthenium, rhodium, osmium, oriridium). Group 10 elements (i.e., platinum or palladium) areparticularly preferred. In one embodiment, the one or more includedplatinum group metals substitute for nickel, another group 10 element,such that the alloy is substantially nickel free (e.g., includes no morethan about 2% nickel by weight). Another embodiment is entirely free ofnickel. In addition, the alloys may include iron, although the amount ofiron is limited to no more than about 20% by weight. In otherembodiments, the amount of iron may be further limited (e.g., no morethan about 10% by weight, no more than about 8% by weight). In someembodiments, the alloys are substantially iron free (e.g., no more thanabout 4% iron by weight). In another embodiment, iron is entirelyabsent.

In an embodiment, a radiopaque stent comprises a cylindrical main bodycomprising a cobalt-based alloy including cobalt, chromium and one ormore platinum group metals selected from the group consisting ofplatinum, palladium, rhodium, iridium, osmium, ruthenium, silver andgold the cobalt-based alloy being substantially free of nickel andcomprising no more than about 20 percent by weight iron.

In an embodiment, the cobalt-based alloy is entirely free of nickel andcomprising no more than about 20 percent by weight iron.

In an embodiment, the cobalt-based alloy being substantially free ofnickel and comprising no more than about 16 percent by weight iron.

In an embodiment, the cobalt-based alloy being substantially free ofnickel and comprising no more than about 10 percent by weight iron.

In an embodiment, the cobalt-based alloy being substantially free ofnickel and comprising no more than about 8 percent by weight iron.

In an embodiment, the cobalt-based alloy being substantially free ofnickel and comprising no more than about 4 percent by weight iron.

In an embodiment, the cobalt-based alloy comprises from about 18 weightpercent to about 50 weight percent cobalt, from about 10 weight percentto about 25 weight percent chromium, from about 10 weight percent toabout 15 weight percent tungsten, from about 0 weight percent to about 2weight percent manganese, from about 0 weight percent to about 3 weightpercent iron, and from about 10 weight percent to about 65 weightpercent of the one or more platinum group metals.

In an embodiment, the cobalt-based alloy comprises from about 40 weightpercent to about 50 weight percent cobalt, from about 15 weight percentto about 25 weight percent chromium, from about 10 weight percent toabout 15 weight percent tungsten, from about 0 weight percent to about 2weight percent manganese, from about 0 weight percent to about 3 weightpercent iron, and from about 10 weight percent to about 35 weightpercent of the one or more platinum group metals.

In an embodiment, the cobalt-based alloy comprises from about 18 weightpercent to about 50 weight percent cobalt, from about 10 weight percentto about 25 weight percent chromium, from about 10 weight percent toabout 15 weight percent tungsten, from about 0 weight percent to about 2weight percent manganese, from about 0 weight percent to about 3 weightpercent iron, and from about 10 weight percent to about 65 weightpercent of the one or more platinum group metals, wherein the one ormore platinum group metals are selected from the group consisting ofplatinum and palladium.

In an embodiment, the cobalt-based alloy comprises from about 18 weightpercent to about 50 weight percent cobalt, from about 10 weight percentto about 25 weight percent chromium, from about 10 weight percent toabout 15 weight percent tungsten, from about 0 weight percent to about 2weight percent manganese, from about 0 weight percent to about 3 weightpercent iron, and from about 10 weight percent to about 65 weightpercent of the one or more platinum group metals, wherein the one ormore platinum group metals comprise from about 10 atomic percent toabout 12 atomic percent of the cobalt-based alloy.

In an embodiment, the cobalt-based alloy comprises from about 22 weightpercent to about 40 weight percent cobalt, from about 15 weight percentto about 25 weight percent chromium, from about 4 weight percent toabout 7 weight percent molybdenum, from about 0 weight percent to about2 weight percent manganese, from about 0 weight percent to about 18weight percent iron, and from about 10 weight percent to about 65 weightpercent of the one or more platinum group metals.

In an embodiment, the cobalt-based alloy comprises from about 22 weightpercent to about 40 weight percent cobalt, from about 15 weight percentto about 25 weight percent chromium, from about 4 weight percent toabout 7 weight percent molybdenum, from about 0 weight percent to about2 weight percent manganese, from about 0 weight percent to about 18weight percent iron, and from about 10 weight percent to about 65 weightpercent of the one or more platinum group metals, wherein the one ormore platinum group metals are selected from the group consisting ofplatinum and palladium.

In an embodiment, the cobalt-based alloy comprises from about 22 weightpercent to about 40 weight percent cobalt, from about 15 weight percentto about 25 weight percent chromium, from about 4 weight percent toabout 7 weight percent molybdenum, from about 0 weight percent to about2 weight percent manganese, from about 0 weight percent to about 18weight percent iron, and from about 10 weight percent to about 65 weightpercent of the one or more platinum group metals, wherein the one ormore platinum group metals comprise from about 14 atomic percent toabout 16 atomic percent of the cobalt-based alloy.

In an embodiment, the cobalt-based alloy comprises from about 22 weightpercent to about 40 weight percent cobalt, from about 15 weight percentto about 25 weight percent chromium, from about 4 weight percent toabout 7 weight percent molybdenum, from about 0 weight percent to about2 weight percent manganese, from about 0 weight percent to about 18weight percent iron, and from about 10 weight percent to about 65 weightpercent of the one or more platinum group metals, wherein the one ormore platinum group metals comprise from about 33 atomic percent toabout 35 atomic percent of the cobalt-based alloy.

In an embodiment, the cobalt-based alloy comprises from about 18 weightpercent to about 39 weight percent cobalt, from about 10 weight percentto about 25 weight percent chromium, from about 5 weight percent toabout 10 weight percent molybdenum, and from about 10 weight percent toabout 65 weight percent of the one or more platinum group metals.

In an embodiment, the cobalt-based alloy comprises from about 18 weightpercent to about 35 weight percent cobalt, from about 15 weight percentto about 25 weight percent chromium, from about 5 weight percent toabout 10 weight percent molybdenum, and from about 40 weight percent toabout 65 weight percent of the one or more platinum group metals.

In an embodiment, the cobalt-based alloy comprises from about 18 weightpercent to about 35 weight percent cobalt, from about 15 weight percentto about 25 weight percent chromium, from about 5 weight percent toabout 10 weight percent molybdenum, and from about 40 weight percent toabout 65 weight percent of the one or more platinum group metals,wherein the one or more platinum group metals are selected from thegroup consisting of platinum and palladium.

In an embodiment, the cobalt-based alloy comprises from about 18 weightpercent to about 35 weight percent cobalt, from about 15 weight percentto about 25 weight percent chromium, from about 5 weight percent toabout 10 weight percent molybdenum, and from about 40 weight percent toabout 65 weight percent of the one or more platinum group metals,wherein the one or more platinum group metals comprise from about 35atomic percent to about 37 atomic percent of the cobalt-based alloy.

In an embodiment, the cobalt-based alloy is formed by providing aninitial alloy comprising nickel and substituting the nickel with the oneor more platinum group metals.

In an embodiment, the cobalt-based alloy is formed by providing aninitial alloy comprising nickel, manganese, and iron and substitutingthe nickel, manganese, and iron with the one or more platinum groupmetals.

In an embodiment, the cobalt-based alloy is formed by providing eachconstituent metal in powder form, mixing the powders together, andcompacting and sintering the mixture of constituent metals in powderform so as to form the cobalt-based alloy.

In an embodiment, the cobalt-based alloy is formed by providing eachconstituent metal in solid form or the powder form of each constituentmetal and then melting the pieces or parts by arc melting, electro-slagremelting, electron beam melting, induction melting, radiant heatmelting, microwave melting, or so forth.

In an embodiment, the one or more platinum group metals consists ofiridium.

In an embodiment, the one or more platinum group metals consists ofiridium, and the cobalt-based alloy is a ternary Co—Cr—Ir alloyconsisting essentially of cobalt, chromium, and iridium in which thechromium is present from about 10 weight percent to about 25 atomicpercent, and the ratio of iridium to cobalt is greater than about 1:1 onan atomic basis.

In an embodiment, the cobalt-based alloy is formed by providing aninitial alloy comprising nickel and cobalt and substituting the nickeland at least a portion of the cobalt with the one or more platinum groupmetals.

In an embodiment, the cobalt-based alloy is formed by providing aninitial alloy comprising nickel and cobalt and substituting the nickeland at least a portion of the cobalt with the one or more platinum groupmetals, wherein the one or more platinum group metals are selected fromthe group consisting of platinum and palladium.

According to another embodiment the main body includes a cobalt-basedalloy that includes cobalt, chromium, and one or more so-calledrefractory metals (i.e., zirconium, niobium, molybdenum, hafnium,tantalum, tungsten, rhenium, silver, or gold). Silver and gold areincluded within this broad classification of refractory metals for sakeof simplicity, as they can be used, even though their meltingtemperatures are significantly lower than the other members of theclass. These two metals could alternatively be termed “precious metals”.In one embodiment, the one or more included refractory metals substitutefor nickel, such that the alloy is substantially nickel free (e.g.,includes no more than about 2% nickel by weight). Another embodiment isentirely free of nickel. In addition, the alloys may include iron,although the amount of iron is limited to no more than about 20% byweight, no more than about 10% by weight, or no more than about 8% byweight. In other embodiments, the alloys are substantially iron free(e.g., no more than about 4% iron by weight). In another embodiment,iron is entirely absent.

Another embodiment of the present invention includes a method forpositioning a stent in a lumen of a living being. The method comprisesproviding a radiopaque stent comprising a cylindrical main body thatincludes a cobalt-based alloy as described above. The cobalt-based alloyis deformable in a ductile manner, rendering the radiopaque stentballoon expandable on a delivery system. The stent is initiallyunexpanded. The stent is transported to a lesion site in the lumenwherein the stent is optionally imaged during transport. The stent isexpanded to contact the lesion. The radiopaque stent is imaged during orafter expanding the stent.

In an embodiment, the cobalt-based alloy may be formed beginning with acobalt-based alloy that does not contain the platinum group metal orrefractory metal, but contains another component to be partially orcompletely substituted (e.g., nickel) with a platinum group metal orrefractory metal. All ingredients would then be melted together (e.g.,arc melting, electro-slag remelting, electron beam melting, inductionmelting, radiant heat melting, microwave melting, or so forth) toproduce an ingot which is then processed by conventional metalworkingmeans to produce tubing or other desired forms. Additional elements suchas iron, silicon, titanium, manganese and cobalt may also be substitutedeither partially or completely in addition to the nickel. For example,the substitution may be made by arc melting the alloy in the presence ofthe substituting element(s). For example, nickel initially presentwithin such a cobalt-chromium alloy may thus be partially or completelysubstituted with a platinum group metal or refractory metal. In someembodiments, a portion of the cobalt may also be substituted.

In another embodiment, powdered elements of the various constituents ofthe revised cobalt-based alloy composition may be mixed together andthen compacted and sintered so as to form the desired alloy by means ofconventional powder metallurgy processing techniques.

In an embodiment, the cobalt-based alloy may include cobalt, chromium,and manganese as an austenitic stabilizer, in addition to the one ormore platinum group metals, refractory metals, and/or precious metalsfor increased radiopacity. Such an alloy may be substantially free ofnickel, may be entirely free of nickel, or at least include a reducedamount of nickel as compared to L-605 (10 weight percent Ni). The alloymay include no or limited amounts of added iron (e.g., no more than 20weight percent iron, no more than 16 weight percent iron, no more than 4weight percent iron, or no added iron). Manganese may be included inamounts from 1 to 25 weight percent, 1 to 17 weight percent, or 1 to 10weight percent. Where manganese and nickel are both included, thecombined weight percentages of Mn+Ni may be from 1 to 25 weight percent,1 to 17 weight percent, or 1 to 10 weight percent. Similarly, thecombined weight percentages of Mn+Ni+Fe may be from 1 to 25 weightpercent, 1 to 17 weight percent, or 1 to 10 weight percent.

In an embodiment, the cobalt-based alloy includes cobalt, chromium, anaustenitic stabilizer for cobalt including a combination of manganeseand optionally nickel, and one or more platinum group metals, refractorymetals, or precious metals. The nickel may be included at less than 5weight percent (if at all) and the alloy may comprise only limited ironcontent (e.g., no more than 20 weight percent) if any iron is includedat all.

In an embodiment, the cobalt-based alloy includes cobalt, chromium, anaustenitic stabilizer for cobalt including a combination of manganeseand nickel, the nickel content being less than that included in L-605alloy (10 weight percent). The alloy includes one or more platinum groupmetals, refractory metals, or precious metals. The nickel may beincluded from 5 to 8 weight percent and the alloy may comprise onlylimited iron content (e.g., no more than 4 weight percent) if any ironis included at all. A combined weight percentage of the manganese andnickel may be from 7 weight percent to 10 weight percent.

In an embodiment, the cobalt-based alloy is one which increasesradiopacity as compared to L-605 by increasing tungsten content, but ina way that ensures a primarily single-phase alloy structure, that ismaintained as face-centered-cubic (FCC), even above the normalsolubility limit of tungsten in such a solid solution. Such an alloy maynot replace any of the nickel present in L-605 with another element, butmay maintain such nickel, even in light of any allergy concerns, inorder to ensure austenitic stability, and FCC phase stability, even atsuper-saturated tungsten content.

Tungsten ordinarily causes separation into two phases in acobalt-chromium alloy at concentrations above 15% tungsten by weight. Byprocessing the alloy during manufacture in a particular manner, it ispossible to increase the tungsten content above this threshold, while atthe same time maintaining the desired content of a primarilysingle-phase FCC crystalline structure by limiting the particle size andvolume fraction or weight percent of any second phase particles. Such aprimarily single-phase structure provides advantageous and desiredmechanical and physical properties (e.g., avoidance of segregated,brittle intermetallic phases such as Co₃W and the like) as compared towhat would normally occur in Co—Cr alloys with elevated tungsten contentas a result of the tungsten causing separation into two coarse phases orformation of a second phase with a large particle size, while at thesame time delivering increased radiopacity as a result of the elevatedtungsten content, all while maintaining the super-saturated tungstencontent in a primarily single-phase FCC structure with only extremelyfine particles of a second phase. Tungsten may be elevated to asuper-saturated level, such as up to about 35% by weight of the alloy,or such as about 20-35% by weight of the alloy. Supersaturation may beattained by heating to form a solid solution and then quickly cooling toavoid formation of a second phase or using powder metallurgy processeswith rapid cooling rates to create very fine powders of the alloy thatlimit the formation of a second phase and the size of second phaseparticles.

The maintenance of the primarily single-phase FCC crystalline structurein the alloy with elevated tungsten can optionally allow for agehardening, which controls the separation of phases such that secondphase exists only as extremely fine particles. By using specifictemperature and time parameters, the alloy may be strengthened throughthe formation of extremely fine precipitates of Co₃W while preservingthe advantages of the primarily single-phase material withsuper-saturated tungsten content.

The alloy may be used to form a radiopaque stent. The radiopaque stentcomprises a cylindrical main body, where the body is formed (e.g.,entirely) from the Co—Cr alloy with super-saturated tungsten content,while maintaining a primarily single-phase FCC microstructure.

The alloy may include chromium (e.g., in a concentration of about 20% byweight), tungsten in a concentration above its solubility limit in acobalt-chromium alloy, such as up to about 35% by weight of the alloy,or such as about 20-35% by weight of the alloy, while also includingnickel in a concentration of 5-15% by weight (e.g., about 10% byweight), manganese in a concentration of 0-5% by weight, iron in aconcentration of 0-5% by weight and other trace elements in aconcentration of 1% maximum, 0.5% maximum, 0.3% maximum, 0.2% maximum,0.1% maximum, 0.05% maximum, or 0.01% maximum. Exemplary trace elementsmay include silicon (e.g., up to about 0.2%), phosphorus (up to about0.02%), and sulfur (up to about 0.02%). Other trace elements typicallypresent in an L-605 alloy (e.g., beryllium, boron, carbon) may beabsent, or at least present at lower concentration than the L-605standard permits. According to a further embodiment of the radiopaqueCo—Cr—Ni—W alloy of the present invention, the alloy is substantiallyfree of molybdenum, carbon and/or other elements not mentioned asincluded, as deliberate alloying elements. The phrase “substantiallyfree” as used herein may include less than 0.05%, less than 0.04%, lessthan 0.03%, less than 0.02%, less than 0.01% or preferably 0% by weight.The alloy of course also includes tungsten in a concentration above itssolubility limit in a cobalt-chromium alloy, such as at 20-35% byweight, but is processed in a manner to ensure that the alloy is of aprimarily homogeneous single-phase with only extremely fine anduniformly dispersed particles of a second phase (e.g., FCC, primarilysingle-phase solid solution). The phrase “primarily single-phase” asused herein may include less than 10% volume fraction of a second phase,less than 7%, less than 5% or less than 3% (e.g., up to about 2%), orless than about 16 weight percent of a second phase, less than 14 weightpercent, less than 10 weight percent, less than 8 weight percent, lessthan 6 weight percent or less than 4 weight percent (e.g., up to about 3weight percent), wherein the particles of the second phase have amaximum or even average particle size of 0.5 μm to 5 μm, including amaximum or average particle size of 3 μm, or a maximum or averageparticle size of less than 15 μm. Any such second phase is finelydispersed, e.g., with a maximum or average particle size that may beless than 10% of the wall thickness of the stent wall. For example,where the wall thickness may be 50 to 100 μm, or 75 to 100 μm, maximumor even average particle size of any finely dispersed second phase maybe less than 10% that of the wall thickness (e.g., 5 μm or less, 4 μm orless, 3 μm or less, 2 μm or less, or even 1 μm or less) so that thepresence of any such second phase has a minimal impact on desiredmechanical properties. Again, a primarily homogeneous single-phasestructure is attained by heating into a molten form to about at least1300° C., about at least 1400° C. or about at least 1500° C. followed byrapid cooling, such as by using powder metallurgy processes with rapidcooling rates to create very fine powders of the alloy that limit theformation of a second phase and the size of second phase particles.

The balance of the alloy is cobalt, e.g., about 30-50% by weight. Astungsten content increases, it may substitute for reduced cobaltcontent. For example, where 20% by weight tungsten is included, cobaltmay be at about 45 to 50%, or 46-48%. Where 25% by weight tungsten isincluded cobalt may be at about 5 percentage points lower (e.g., 40 to45%, or 41 to 43% by weight). Similarly, at 30% by weight tungsten,cobalt may be another 5 percentage points lower (e.g., 35 to 40%, or 36to 38% by weight). At 35% by weight tungsten, which is extremelysuper-saturated in tungsten content, cobalt may be another 5 percentagepoints lower (e.g., 30% to 35%, or 31 to 33% by weight). Thus in anembodiment including 20% tungsten, the tungsten/cobalt weight percentratio (W/Co) may be about from 0.35 to 0.5, or from 0.4 to about 0.45,in an embodiment including 25% tungsten, the W/Co ratio may be fromabout 0.5 to 0.7, or from about 0.57 to 0.63. In an embodiment including30% tungsten, the W/Co ratio may be from about 0.7 to about 0.9, or from0.79 to 0.85, and in an embodiment including 30% Tungsten, the W/Co wt.% ratio may actually be 1 or greater, such as from 1 to 1.2, or from1.07 to 1.13.

In an embodiment, the alloy may comprise no more than 1%, no more than0.5%, no more than 0.4%, no more than 0.3%, no more than 0.2%, no morethan 0.1%, no more than 0.05%, no more than 0.03%, or no more than 0.02%of any of silicon, phosphorous or sulfur by weight.

A primarily homogeneous single-phase structure is attained by heatinginto a molten form to about at least 1300° C., about at least 1400° C.or about at least 1500° C. followed by rapid cooling, such as by usingpowder metallurgy processes with rapid cooling rates to create very finepowders of the alloy that limit the formation of a second phase and thesize of second phase particles.

The present application incorporates by reference in its entirety,another application by Applicant 62/914,806, filed the same day as thepresent application.

Features from any of the disclosed embodiments may be used incombination with one another, without limitation. For example, any ofthe compositional limitations described with respect to one embodiment(e.g., limited iron content, limited content of other elements, or thelike) may be present in any of the other described embodiments. Inaddition, other features and advantages of the present disclosure willbecome apparent to those of ordinary skill in the art throughconsideration of the following detailed description and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other advantages and features of thepresent disclosure, a more particular description will be rendered byreferences to specific embodiments thereof, which are illustrated in theappended drawings. It is appreciated that these drawings depict onlytypical embodiments of the invention and are therefore not to beconsidered limiting of its scope. The present disclosure will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings in which:

FIG. 1 is an elevational view, partially in section, of a radiopaquestent according to an embodiment of the present invention mounted on adelivery catheter and disposed within a damaged lumen;

FIG. 2 is an elevational view, partially in section, showing theradiopaque stent of FIG. 1 within a damaged lumen;

FIG. 3 is an elevational view, partially in section, showing theradiopaque stent of FIG. 1 expanded within the lumen after withdrawal ofthe delivery catheter;

FIGS. 4A and 4B show a phase diagram for cobalt-chromium;

FIGS. 5A and 5B show a phase diagram for cobalt-nickel;

FIGS. 6A and 6B show a phase diagram for nickel-chromium;

FIGS. 7A and 7B show a phase diagram for cobalt-tungsten;

FIGS. 8A and 8B show a phase diagram for chromium-tungsten;

FIGS. 9A and 9B show a phase diagram for nickel-tungsten;

FIGS. 10A and 10B show a phase diagram for molybdenum-cobalt;

FIGS. 11A and 11B show a phase diagram for chromium-molybdenum;

FIGS. 12A and 12B show a phase diagram for nickel-molybdenum;

FIGS. 13A and 13B show a phase diagram for silver-cobalt;

FIGS. 14A and 14B show a phase diagram for chromium-silver;

FIGS. 15A and 15B show a phase diagram for silver-molybdenum;

FIGS. 16A and 16B show a phase diagram for gold-cobalt;

FIGS. 17A and 17B show a phase diagram for gold-chromium;

FIGS. 18A and 18B show a phase diagram for gold-molybdenum;

FIGS. 19A and 19B show a phase diagram for gold-tungsten;

FIGS. 20A and 20B show a phase diagram for cobalt-hafnium;

FIGS. 21A and 21B show a phase diagram for chromium-hafnium;

FIGS. 22A and 22B show a phase diagram for molybdenum-hafnium;

FIGS. 23A and 23B show a phase diagram for hafnium-tungsten;

FIGS. 24A and 24B show a phase diagram for molybdenum-cobalt;

FIGS. 25A and 25B show a phase diagram for chromium-molybdenum;

FIGS. 26A and 26B show a phase diagram for molybdenum-tungsten;

FIGS. 27A and 27B show a phase diagram for niobium-cobalt;

FIGS. 28A and 28B show a phase diagram for chromium-niobium;

FIGS. 29A and 29B show a phase diagram for molybdenum-niobium;

FIGS. 30A and 30B show a phase diagram for niobium-tungsten;

FIGS. 31A and 31B show a phase diagram for cobalt-rhenium;

FIGS. 32A and 32B show a phase diagram for chromium-rhenium;

FIGS. 33A and 33B show a phase diagram for molybdenum-rhenium;

FIGS. 34A and 34B show a phase diagram for rhenium-tungsten;

FIGS. 35A and 35B show a phase diagram for cobalt-tantalum;

FIGS. 36A and 36B show a phase diagram for chromium-tantalum;

FIGS. 37A and 37B show a phase diagram for molybdenum-tantalum;

FIGS. 38A and 38B show a phase diagram for tantalum-tungsten;

FIGS. 39A and 39B show a phase diagram for cobalt-tungsten;

FIGS. 40A and 40B show a phase diagram for chromium-tungsten;

FIGS. 41A and 41B show a phase diagram for molybdenum-tungsten;

FIGS. 42A and 42B show a phase diagram for cobalt-zirconium;

FIGS. 43A and 43B show a phase diagram for zirconium-chromium;

FIGS. 44A and 44B show a phase diagram for molybdenum-zirconium;

FIGS. 45A and 45B show a phase diagram for tungsten-zirconium;

FIGS. 46A and 46B show a phase diagram for cobalt-iron;

FIGS. 47A and 47B show a phase diagram for cobalt-palladium;

FIGS. 48A and 48B show a phase diagram for cobalt-platinum;

FIGS. 49A and 49B show a phase diagram for chromium-iron;

FIGS. 50A and 50B show a phase diagram for chromium-palladium;

FIGS. 51A and 51B show a phase diagram for chromium-platinum;

FIGS. 52A and 52B show a phase diagram for iron-palladium;

FIGS. 53A and 53B show a phase diagram for iron-platinum; and

FIGS. 54A and 54B show a phase diagram for palladium-platinum.

FIG. 55 shows an additional phase diagram for cobalt-tungsten, inaddition to those of FIGS. 7A-7B and 39A-39B.

FIG. 56 shows an additional phase diagram for chromium-tungsten, inaddition to those of FIGS. 8A-8B and 40A-40B.

FIG. 57 shows an additional phase diagram for nickel-tungsten, inaddition to that of FIGS. 9A-9B.

FIG. 58 shows a ternary phase diagram for cobalt-nickel-tungsten at500K.

FIG. 59 shows a ternary phase diagram for cobalt-nickel-tungsten at1000K.

FIG. 60 shows a ternary phase diagram for cobalt-nickel-tungsten at1500K.

FIG. 61a shows an SEM image of an as cast ingot of a Co—Cr—Ni—W alloyhaving 20% W content and a coarse second phase.

FIG. 61b shows an SEM image of a Co—Cr—Ni—W alloy according to FIG. 61aat an increased resolution.

FIG. 61c shows an SEM image of a Co—Cr—Ni—W alloy according to FIG. 61aat an increased resolution.

FIG. 62a shows an SEM image of an as cast ingot of a Co—Cr—Ni—W alloyhaving 25% W content and a coarse second phase.

FIG. 62b shows an SEM image of a Co—Cr—Ni—W alloy according to FIG. 62aat an increased resolution

FIG. 62c shows an SEM image of a Co—Cr—Ni—W alloy according to FIG. 62aat an increased resolution.

DETAILED DESCRIPTION

I. Introduction

Embodiments of the present invention are directed to radiopaque cobaltalloys, radiopaque implantable structures (e.g., stents) and relatedmethods of manufacture and use. A radiopaque stent may include acylindrical main body comprising a radiopaque cobalt-based alloyincluding cobalt, chromium, and one or more platinum group metals (i.e.,one or more of platinum, palladium, ruthenium, rhodium, osmium, oriridium), refractory metals (i.e., zirconium, niobium, molybdenum,hafnium, tantalum, tungsten, rhenium, silver, or gold), or combinationsthereof. Advantageously the alloys are substantially nickel free (e.g.,include no more than about 2% by weight nickel, more typically no morethan 1% nickel by weight). In one embodiment, the alloy is entirely freeof nickel. By entirely free of nickel, it will be understood that minutetrace fractions of nickel may still be present in some embodiments basedon the fact that the alloy includes cobalt, and it can be verydifficult, if not a practical impossibility to entirely separate traceamounts of nickel from the cobalt. In any event, where the alloy is“entirely” free of nickel, no nickel is intentionally added to thealloy.

Some patients exhibit an allergic reaction to nickel, and so providing anickel-free alloy is advantageous as it increases the biocompatibilityof the alloy. In addition, the inclusion of the nickel limits the degreeof radiopacity that may be achieved. In addition, the alloy preferablydoes not include a large fraction of iron. For example, in oneembodiment, the alloy includes no more than about 20% by weight iron,more preferably no more than about 16% by weight iron, no more thanabout 10% by weight iron, or no more than about 8% by weight iron. Inanother embodiment, iron is present, if at all, in an amount not greaterthan about 4% by weight, more typically not greater than about 3% byweight. In another embodiment, the alloy is iron-free. Similar to themeaning of nickel-free, the term iron-free means that no iron isintentionally added to the alloy, although trace amounts may be presentas impurities carried in the other elements. Limiting the amount of ironwithin the alloy allows other elements to be present that provide forbetter radiopacity and corrosion resistance than does iron. In addition,it may reduce any magnetic characteristics of the resulting metal alloy,which may be helpful in conjunction with MRI and/or other imagingtechniques.

Another embodiment of the present invention is directed to animplantable radiopaque device, such as a stent, that is formed of aradiopaque cobalt-chromium-nickel-tungsten (Co—Cr—Ni—W) alloy, in whichthe tungsten content is specifically elevated above its normalsolubility limit in cobalt-chromium, but in a way to ensure that thealloy maintains a primarily single-phase, FCC microstructure. Whiletungsten typically separates into two phases at concentrations of about15% by weight at typically employed thermal processing conditions,conditions employed according to the present disclosure allow elevatedtungsten concentrations, e.g., from 20-35% tungsten by weight. Byincreasing the amount of tungsten in the alloy while retaining aprimarily single-phase, FCC microstructure, the alloy enables a stentwith a higher radiopacity without the use of high cost platinum groupmetals or precious metals, or other refractory metals, while maintainingadvantageous mechanical properties, chemical processing behavior andcorrosion performance associated with a single-phase material.

II. Radiopaque Stent and Cobalt-Based Alloy Embodiments

According to various embodiments, the radiopaque stent is imagableduring fluoroscopy. Due to the enhanced radiopacity, the entire stent isbetter observed by the practitioner placing the stent. The imageobserved by the practitioner is thus less likely to be too faint due toinsufficient radiopacity or the lumen is not visible from excessiveradiopacity. Because of the improved image, the stent is more easily andaccurately positioned and manipulated within a lumen of a patient.Because the radiopaque composition from which the stent is formed hasgreater radiopacity per unit thickness than alternative alloys, thestent may also be formed at thinner thickness all the while providing adesired level of radiopacity performance. An additional advantage to thebetter radiopacity is the visualization of the stent and the underlyingvessel during follow-up examinations by the practitioner. Because theentire stent is radiopaque, the diameter and length of the stent arereadily discerned by the practitioner. Also, because the stent itself ismade of the radiopaque alloy, the stent does not have problemsassociated with radiopaque coatings, such as cracking, separation, orcorrosion. Also, because the entire stent is radiopaque, the stent doesnot require extra markers with their attendant issues. In an embodiment,such coatings or markers may be absent.

The strength of the alloy material is sufficient that the stent may bemanufactured with a low profile. The low profile of the disclosedcobalt-based alloy stents, coupled with its enhanced radiopacity rendersthe stent easily deliverable with easier observation and detectionthroughout its therapeutic use than stents heretofore available. A stentconstructed of the specific contemplated cobalt-based alloys can be madethinner than one of stainless steel without sacrificing fluoroscopicvisibility. The low profile of the disclosed cobalt-based stents rendersthe stent more easily deliverable with greater flexibility.

Furthermore, improved radiopacity of the low profile stent increasesdeliverability of the stent and offers additional performance advantagesin the form of decreased fluid mechanics disturbances to blood flow andmore rapid reendothelialization. Improved radiopacity assists thepractitioner in placing the device precisely. Inflation of the stent isbetter monitored because the stent is more readily visible to thepractitioner. This visibility reduces the incidence and probability ofan under-deployed stent. Further, in-stent restenosis may be moreaccurately monitored as the stent and an injected contrast agent areable to be imaged simultaneously. Unlike some stents, the disclosedstents do not produce an image which is too bright, thereby obscuringimaging of the underlying vessel morphology.

Many cobalt-based alloys, although very strong, have insufficientductility for use in a stent. The cobalt-based alloys described hereinpreferably have at least 20% or greater elongation and thereby achieveadequate stent expansion. Some of the disclosed cobalt-based alloys alsoinclude elements such as tungsten or molybdenum. These elements not onlystrengthen, but also contribute to the overall excellent radiopacity ofthe cobalt-based alloy (particularly in the case of tungsten). Theseelements (e.g., tungsten or molybdenum) may also improve corrosionresistance and a resistance to oxidation at high temperatures of thecobalt-based alloy.

For example, cobalt-chromium alloy L-605, covered by ASTM standard F90,includes about 15% by weight tungsten (e.g., just below the solubilitylimit of tungsten in cobalt-chromium). Alloy L-605 has a minimumultimate tensile strength of 125 ksi, a minimum yield strength of 45 ksiand a minimum total elongation of 30%. According to one embodiment ofthe invention, the alloy is similar to L-605, in which substantially allof the nickel of L-605 has been replaced with a platinum group metal, arefractory metal, or combinations thereof. For example, alloy L-605contains about 10% by weight nickel. By substituting the nickel with aplatinum group metal or refractory metal, the relative radiopacity ofthe resulting alloy is increased relative to alloy L-605, and theresulting alloy is advantageously nickel free or substantially nickelfree. Other embodiments described herein do not replace the nickel, butinclude elevated levels of the refractory metal tungsten, in particular.

Another exemplary alloy which may be similarly modified is Elgiloy,covered by ASTM standard F1058 Grade 1. Phynox is an alternative alloycomposition similar to that of Elgiloy. Phynox is covered by ASTMstandard F1058 Grade 2. Elgiloy is a cobalt-chromium alloy containingabout 40% by weight cobalt, about 20% by weight chromium, about 16% byweight iron, about 15% by weight nickel, about 7% by weight molybdenum,and about 2% by weight manganese. Phynox is similar, but the manganeseis replaced with iron. The nickel may be substituted with a platinumgroup metal or refractory metal so as to result in an alloy havingincreased relative radiopacity and that is nickel free or substantiallynickel free. In another embodiment, the platinum group metal orrefractory metal may also replace all or a part of the iron and/ormanganese.

Another exemplary alloy which may be similarly modified is MP-35N,covered by ASTM standard F562. MP-35N is a cobalt-chromium alloycontaining about 35% by weight cobalt, about 20% by weight chromium,about 35% by weight nickel, about 10% by weight molybdenum, and about 1%maximum iron. The nickel may be substituted with a platinum group metalor refractory metal so as to result in an alloy having increasedrelative radiopacity and that is nickel free or substantially nickelfree. In another embodiment, the platinum group metal or refractorymetal may replace all or a part of the iron as well.

In additional embodiments, upon completely replacing the nickel, aportion of the cobalt may also be replaced by the platinum groupmetal(s) or refractory metal(s), based on the overall increase inradiopacity that is desired. This substitution may be performed for anycobalt-based alloy, including those described above. To maintain asingle-phase microstructure, it is suggested that the cobalt besubstituted with a platinum group element or refractory metal that hassubstantially complete mutual solid solubility with cobalt. Furthermore,in some embodiments, some of the chromium or another element in theknown alloy may also be replaced.

Atomic substitution takes an “atom for atom” approach in alloymodification by employing atomic weight. Atomic weight is commonlyunderstood to be weight per mole of atoms. Atomic substitution maintainsthe stoichiometry of the original alloy when substituting, which may bean important approach when working with ordered alloys and whenmaintaining a particular phase structure. Atomic substitution may bemore commonly understood in the art than volumetric substitution.

Volumetric substitution accounts for both the atomic radii and thecrystal structure that the element naturally takes in the solid form, byemploying atomic volume. Atomic volume is commonly understood to bevolume per mole of atoms in the solid phase. This approach providesinsight into effects on the host lattice by the substituting atom(s).This approach may allow for better retaining and understanding of theworkability and mechanical strength of the modified alloy.

Substitution on a weight percent basis results in alloys that havecomparatively less of the platinum group elements (or refractoryelements), as all of them have greater atomic weight and density thanthe majority of elements being substituted for in the originalcobalt-based alloys. Utilizing weight percent for substitution may bemore typically employed for cobalt-based alloys where the elements havesimilar atomic weights, such as stainless steels, which are comprisedprimarily of iron, chromium and nickel.

Due to the low atomic weight of nickel compared to that of the platinumgroup metals (and somewhat less so as compared to the refractorymetals), it will readily be realized that substituting for nickel wouldproduce significantly different overall alloy compositions if thesubstitution were based on weight percentage as compared to atomicpercentage. This is an important consideration with regard toradiopacity, because the attenuation of x-rays by a given material islargely dictated by the energy of the electron orbitals surrounding itsatoms and their nuclei. Elements with more massive nuclei, andcorrespondingly higher energy orbitals, attenuate x-rays to a muchgreater extent than those with lighter nuclei, which explains why metalslike tantalum, tungsten, platinum, and gold are inherently moreradiopaque than lighter metals like chromium, iron, cobalt, and nickel.Thus, when substituting a platinum group metal (or a refractory metal)for nickel in a given alloy, the resulting impact on radiopacity isconsiderably greater when the nickel is replaced on an atom-for-atombasis rather than gram-for-gram. The impact of a given alloying elementon many of an alloy's chemical properties, such as corrosion resistance,also depends on the atomic percentage present.

While nickel is the preferred element to be substituted by a platinumgroup or refractory metal for biocompatibility reasons, in someembodiments other elements in commercial cobalt-based alloys may bereplaced (i.e., substituted), particularly if greater radiopacity isdesired. Note that iron and manganese are minor alloying elements inL-605, iron and silicon are minor alloying elements in Elgiloy, and ironand titanium are minor alloying elements in MP-35N. These elements arenot considered essential, with regard to corrosion behavior androom-temperature mechanical properties, especially if other impuritiessuch as carbon and sulfur are held to a minimum, and therefore could bereplaced by more of the platinum group metal(s) (or refractory metal(s))and thereby simplify the overall composition while further increasingradiopacity. Should radiopacity still be insufficient after nickel andthese minor alloying elements have been fully substituted, a portion ofthe cobalt could also be replaced by the platinum group metal(s) orrefractory metals. This strategy would more likely be applied tocobalt-based alloys that contain lesser amounts of nickel, such asL-605.

Nickel plays an important role in commercial cobalt-based alloys. As iniron-based stainless steels, nickel serves as an “austenite stabilizer”in cobalt-based alloys. That is, nickel suppresses cobalt's allotropictransformation from a face-centered-cubic (“FCC”) crystal structure athigh temperatures to a hexagonal-close-packed (“HCP”) structure at lowtemperatures. In pure cobalt, this transformation naturally occurs ataround 422° C. The addition of nickel significantly reduces cobalt'stransformation temperature, thereby favoring the FCC structure which, ingeneral, is a more ductile and more creep-resistant crystal structurethan HCP. Therefore, when substituting nickel with another element, itis important that the replacement also serve as an austenite stabilizer.

By way of example, palladium immediately suppresses cobalt's FCC-to-HCPtransformation temperature at relatively small addition levels, whereasplatinum, rhodium and iridium initially raise and then ultimately lowerthe transformation temperature as alloying levels rise, while rutheniumand osmium continuously raise cobalt's transformation temperature astheir levels rise. Similar considerations apply in the potentialsubstitution of refractory metals for nickel. Thus, the particularplatinum group and/or refractory metal(s) selected and theirsubstitution levels are important considerations with regard to thefinal crystal structure(s) that will be obtained at ambienttemperatures. As further described herein, one issue with tungstenaddition is attempting to increase tungsten content above its solubilitylimit (about 15% by weight) normally causes phase separation in whichthe tungsten separates into two phases in the cobalt-chromium solutionmatrix.

As explained in further detail below in conjunction with Tables 7-10 andExamples 90-132, manganese can serve to suppress cobalt's FCC-to-HCPtransformation, and as such, may be included as an austeniticstabilizer.

Chromium also plays an important role in commercial cobalt-based alloys.As in iron-based stainless steels, chromium is also a powerful corrosioninhibitor in cobalt-based alloys. Corrosion and elevated-temperatureoxidation behavior are substantially improved by the stable, tightlyadhering chromium oxide layer that spontaneously forms when chromiumcontaining cobalt-based alloys are exposed to air or other oxidizingenvironments. This layer serves to protect these alloys in a variety ofotherwise corrosive environments, including saline and blood. For thisreason, it is beneficial when substituting nickel and possibly otherelements with platinum group and/or refractory metals that the resultingalloy composition contain sufficient chromium that adequate corrosionresistance is maintained. Iron-based austenitic stainless steels liketypes 304 and 316 typically contain approximately 18% by weightchromium, whereas L-605, Elgiloy, and MP-35N each contain about 20% byweight. Thus, it is not recommended that platinum group metals and/orrefractory metals replace significant amounts of the chromium present incommercial cobalt-based alloys. Where additional corrosion resistance iswarranted, the chromium level may be increased (e.g., to about 25% byweight).

In any case, chromium is present in sufficient amount to inhibitcorrosion. Some alloy embodiments may include chromium fractions wellbelow 20% by weight while still achieving this purpose (e.g., at leastabout 10% by weight, or from about 10% to about 15% by weight). Specificexamples of such alloys are found in Table 5 and Examples 78-89. Thismay be possible particularly where the atomic percentage of chromiumremains relatively high (e.g., at least about 20 atomic percent, or atleast about 25 atomic percent). The weight percentages are lower inExamples 78-89 because the very dense platinum is included in highfractions.

Generally, alloys based on an L-605 alloy in which the nickel has beenreplaced on either an atomic or volumetric basis with a platinum groupmetal may include about 18 weight percent to about 50 weight percentcobalt (e.g., in one embodiment about 40 to about 50 weight percentcobalt), about 10 weight percent to about 25 weight percent chromium(e.g., in one embodiment about 15 weight percent to about 25 weightpercent chromium, about 15 to about 20 weight percent chromium, or about20 weight percent chromium), about 10 weight percent to about 15 weightpercent tungsten, about 0 weight percent to about 2 weight percentmanganese, about 0 weight percent to about 3 weight percent iron, andabout 10 weight percent to about 65 weight percent of a platinum groupmetal. One embodiment may include about 10 weight percent to about 35weight percent of a platinum group metal (i.e., platinum, palladium,ruthenium, rhodium, osmium, iridium, or combinations thereof). Examplesof such materials are further described below in conjunction with Table1 and Examples 1-12. Trace elements included within this alloy may notbe shown unless they are called out for substitutional purposes.

Generally, alloys based on an ASTM F1058 alloy (e.g., Elgiloy or Phynox)in which at least the nickel has been replaced (e.g., iron and/ormanganese may also be replaced) on an atomic basis with a platinum groupmetal may include about 22 weight percent to about 40 weight percentcobalt, about 10 weight percent to about 25 weight percent chromium(e.g., in one embodiment about 15 weight percent to about 25 weightpercent chromium, about 15 to about 20 weight percent chromium, or about20 weight percent chromium), about 4 weight percent to about 7 weightpercent molybdenum, about 0 weight percent to about 2 weight percentmanganese, about 0 weight percent to about 18 weight percent iron, andabout 10 weight percent to about 65 weight percent of a platinum groupmetal (i.e., platinum, palladium, ruthenium, rhodium, osmium, iridium,or combinations thereof). One example may include about 15 weightpercent to about 65 weight percent of a platinum group metal. Examplesof such materials are further described below in conjunction with Table2 and Examples 13-20. Trace elements included within this alloy may notbe shown unless they are called out for substitutional purposes.

Another alloy based on an ASTM F1058 alloy could replace the nickel witha refractory metal (e.g., silver, gold, hafnium, niobium, rhenium,tantalum, molybdenum, zirconium, or combinations thereof), and includeweight fractions as described above, but in which the refractory metal(rather than a platinum group metal) is included from about 10 weightpercent to about 65 weight percent, or from about 15 weight percent toabout 65 weight percent.

Generally, alloys based on an MP-35N alloy in which the nickel has beenreplaced on an atomic percentage basis by a platinum group metal mayinclude about 18 weight percent to about 39 weight percent cobalt (e.g.,one embodiment may include about 18 to about 35 weight percent cobalt),about 10 weight percent to about 25 weight percent chromium (e.g., inone embodiment about 15 weight percent to about 25 weight percentchromium, about 15 to about 20 weight percent chromium, about 10 toabout 21 weight percent chromium, or about 20 weight percent chromium),about 5 weight percent to about 10 weight percent molybdenum, and about10 weight percent to about 65 weight percent of a platinum group metal(i.e., platinum, palladium, ruthenium, rhodium, osmium, iridium, orcombinations thereof). One embodiment may include about 40 to about 65weight percent of a platinum group metal. Examples of such materials arefurther described below in conjunction with Table 3 and Examples 21-24.Trace elements included within this alloy may not be shown unless theyare called out for substitutional purposes.

Generally, alloys based on an L-605 alloy in which the nickel has beenreplaced on a weight percentage basis with a refractory metal mayinclude about 18 weight percent to about 55 weight percent cobalt (e.g.,in one embodiment about 20 to about 55 weight percent cobalt), about 15weight percent to about 25 weight percent chromium (e.g., in oneembodiment about 20 weight percent chromium), about 0 weight percent toabout 15 weight percent tungsten, and about 10 weight percent to about60 weight percent of a substituting refractory metal selected from thegroup consisting of silver, gold, hafnium, niobium, rhenium, tantalum,molybdenum, zirconium, or combinations thereof. One embodiment mayinclude about 10 weight percent to about 45 weight percent of thesubstituting refractory metal (i.e., silver, gold, hafnium, niobium,rhenium, tantalum, molybdenum, zirconium, or combinations thereof).Examples of such alloys are further described below in conjunction withTable 1 and Examples 25-28, 31-33, 36-38, 41-43, 46-47, 50-52, 55-57,60, 65-66, and 69. Other trace elements (e.g., manganese, iron, etc.)may be present in small amounts of about 0 to about 3 percent by weight.Trace elements included within this alloy may not be shown unless theyare called out for substitutional purposes. Other embodiments (Examples133-136) described herein maintain the L-605 nickel content, andincrease tungsten content above its normal solubility limit, while atthe same time maintaining a primarily single-phase FCC microstructure,by ensuring particular processing conditions are used in manufacture.

L-605 alloy already contains about 15 weight percent tungsten. An alloybased on an L-605 alloy in which the nickel has been replaced on aweight percentage basis with the refractory metal tungsten may includeabout 18 weight percent to about 55 weight percent cobalt (e.g., in oneembodiment about 20 to about 55 weight percent cobalt), about 15 weightpercent to about 25 weight percent chromium (e.g., in one embodimentabout 20 weight percent chromium), and about 25 weight percent to about60 weight percent tungsten. One embodiment may include about 25 weightpercent to about 45 weight percent of the substituting refractory metaltungsten. Examples of such tungsten alloys are further described belowin conjunction with Table 1 and Examples 61-62. Other trace elements(e.g., manganese, iron, etc.) may be present in small amounts of about 0to about 3 percent by weight. Other examples are also disclosed(Examples 133-136), also based on L-605, but where the nickel fractionis maintained, and tungsten concentration is increased in specificmanner in which primarily single-phase characteristics are maintained.

Generally, alloys based on an MP-35N alloy in which the nickel has beenreplaced on a weight percentage basis by a refractory metal may includeabout 18 weight percent to about 39 weight percent cobalt (e.g., oneembodiment may include about 20 to about 35 weight percent cobalt),about 15 weight percent to about 25 weight percent chromium (e.g., oneembodiment may include about 20 weight percent chromium), about 0 weightpercent to about 10 weight percent molybdenum, and about 35 weightpercent to about 60 weight percent of a substituting refractory metal(i.e., silver, gold, hafnium, niobium, rhenium, tantalum, tungsten,zirconium, or combinations thereof). One embodiment may include about 35to about 50 weight percent of a substituting refractory metal. Examplesof such materials are further described below in conjunction with Table3 and Examples 29-31, 34-36, 39-41, 44-45, 48-50, 53-55, 58-60, 63-64,and 67-69. Trace elements included within this alloy may not be shownunless they are called out for substitutional purposes.

MP-35N alloy already contains about 10 weight percent molybdenum. Analloy based on an MP-35N alloy in which the nickel has been replaced ona weight percentage basis with the refractory metal molybdenum mayinclude about 18 weight percent to about 39 weight percent cobalt (e.g.,in one embodiment about 20 to about 35 weight percent cobalt), about 15weight percent to about 25 weight percent chromium (e.g., in oneembodiment about 20 weight percent chromium), and about 45 weightpercent to about 60 weight percent molybdenum. Examples of suchmolybdenum alloys are further described below in conjunction with Table1 and Examples 44-45. Other trace elements (e.g., manganese, iron, etc.)may be present in small amounts of about 0 to about 3 percent by weight.

One type of radiopaque stent design embodiment is a high precisionpatterned cylindrical device. This device is illustrated generally at 10in FIG. 1. The stent 10 typically comprises a plurality of radiallyexpanded cylindrical elements 12 disposed generally coaxially andinterconnected by elements 13 disposed between adjacent cylindricalelements.

For some embodiments, the stent 10 is expanded by a delivery catheter11. The delivery catheter 11 has an expandable portion or a balloon 14for expanding of the stent 10 within an artery 15. The delivery catheter11 onto which the stent 10 is mounted may be similar to a conventionalballoon dilation catheter used for angioplasty procedures. The artery15, as shown in FIG. 1, has a dissected lining 16 which has occluded aportion of the arterial passageway.

Each radially expandable cylindrical element 12 of the radiopaque stent10 may be independently expandable. Therefore, the balloon 14 may beprovided with an inflated shape other than cylindrical, e.g., tapered,to facilitate implantation of the stent 10 in a variety of body lumenshapes.

The delivery of the radiopaque stent 10 is accomplished by mounting thestent 10 onto the inflatable balloon 14 on the distal extremity of thedelivery catheter 11. The catheter-stent assembly is introduced withinthe patient's vasculature using conventional techniques through aguiding catheter which is not shown. A guidewire 18 is disposed acrossthe damaged arterial section and then the catheter-stent assembly isadvanced over a guidewire 18 within the artery 15 until the stent 10 isdirectly under detached lining 16 of the damaged arterial section. Theballoon 14 of the catheter is expanded, expanding the stent 10 againstthe artery 15, which is illustrated in FIG. 2. While not shown in thedrawing, the artery 15 may preferably be expanded slightly by theexpansion of the stent 10 to seat or otherwise fix the stent 10 toprevent movement. In some circumstances during the treatment of astenotic portion of an artery, the artery may have to be expandedconsiderably in order to facilitate passage of blood or other fluidtherethrough. This expansion is easily observable by the practitionerwith the disclosed radiopaque stents.

The stent 10 serves to hold open the artery 15 after the catheter 11 iswithdrawn, as illustrated in FIG. 3. Due to the formation of the stent10 from the elongated tubular member, the undulating component of thecylindrical elements of the stent 10 is relatively flat in transversecross section so that when the stent is expanded, the cylindricalelements are pressed into the wall of the artery 15 and as a result donot interfere with the blood flow through the artery 15. The cylindricalelements 12 of the stent 10 which are pressed into the wall of theartery 15 are eventually covered with endothelial cell growth whichfurther minimizes blood flow interference. The undulating pattern of thecylindrical sections 12 provides good characteristics to prevent stentmovement within the artery. Furthermore, the closely spaced cylindricalelements at regular intervals provide uniform support for the wall ofthe artery 15, and consequently are well adapted to tack up and hold inplace small flaps or dissections in the wall of the artery 15 asillustrated in FIGS. 2-3. The undulating pattern of the radiopaque stentis readily discernable to the practitioner performing the procedure.

Additional details of exemplary stents are disclosed in U.S. Pat. No.7,250,058, incorporated herein by reference in its entirety.

TABLE 1 ASTM F90 L-605 Alloy Weight Atomic Volume Element PercentPercent Percent Cobalt 53.4 53.9 51.6 Chromium 20 24.4 25.2 Tungsten 155.2 7.1 Nickel 10 10.8 10.2 Manganese (maximum) 1.5 2.3 2.4 Iron(maximum) 0.1 3.4 3.5

Examples 1-12 below are based on the nominal compositions of the ASTMF90 L-605 Alloy of Table 1 in which only the nickel has been replaced onan atomic substitution basis or a volumetric substitution basis with aplatinum group metal. Trace elements such as beryllium, boron, carbon,phosphorus, silicon, and sulfur are not listed.

Example 1—ASTM F90 L-605 Alloy with Atomic Substitution of Nickel withPlatinum

Element Atomic Percent Weight Percent Cobalt 53.9 40.6 Chromium 24.416.2 Tungsten 5.2 12.2 Platinum 10.8 27.0 Manganese (maximum) 2.3 1.6Iron (maximum) 3.4 2.4

Example 2—ASTM F90 L-605 Alloy with Volumetric Substitution of Nickelwith Platinum

Element Weight Percent Volume Percent Cobalt 43.8 51.6 Chromium 17.525.2 Tungsten 13.2 7.1 Platinum 21.1 10.2 Manganese (maximum) 1.8 2.4Iron (maximum) 2.6 3.5

Example 3—ASTM F90 L-605 Alloy with Atomic Substitution of Nickel withPalladium

Element Atomic Percent Weight Percent Cobalt 53.9 46.2 Chromium 24.418.5 Tungsten 5.2 13.9 Palladium 10.8 16.8 Manganese (maximum) 2.3 1.8Iron (maximum) 3.4 2.8

Example 4—ASTM F90 L-605 Alloy with Volumetric Substitution of Nickelwith Palladium

Element Volume Percent Weight Percent Cobalt 51.6 48.3 Chromium 25.219.3 Tungsten 7.1 14.4 Palladium 10.2 13.1 Manganese (maximum) 2.4 2Iron (maximum) 3.5 2.9

Example 5—ASTM F90 L-605 Alloy with Atomic Substitution of Nickel withRhodium

Element Atomic Percent Weight Percent Cobalt 53.9 46.5 Chromium 24.418.6 Tungsten 5.2 13.9 Rhodium 10.8 16.3 Manganese (maximum) 2.3 1.9Iron (maximum) 3.4 2.8

Example 6—ASTM F90 L-605 Alloy with Volumetric Substitution of Nickelwith Rhodium

Element Volume Percent Weight Percent Cobalt 51.6 48.1 Chromium 25.219.2 Tungsten 7.1 14.4 Rhodium 10.2 13.4 Manganese (maximum) 2.4 2 Iron(maximum) 3.5 2.9

Example 7—ASTM F90 L-605 Alloy with Atomic Substitution of Nickel withIridium

Element Atomic Percent Weight Percent Cobalt 53.9 40.7 Chromium 24.416.3 Tungsten 5.2 12.3 Iridium 10.8 26.7 Manganese (maximum) 2.3 1.6Iron (maximum) 3.4 2.4

Example 8—ASTM F90 L-605 Alloy with Volumetric Substitution of Nickelwith Iridium

Element Volume Percent Weight Percent Cobalt 51.6 43.4 Chromium 25.217.4 Tungsten 7.1 13 Iridium 10.2 21.9 Manganese (maximum) 2.4 1.7 Iron(maximum) 3.5 2.6

Example 9—ASTM F90 L-605 Alloy with Atomic Substitution of Nickel withRuthenium

Element Atomic Percent Weight Percent Cobalt 53.9 46.6 Chromium 24.418.7 Tungsten 5.2 14.0 Ruthenium 10.8 16.1 Manganese (maximum) 2.3 1.9Iron (maximum) 3.4 2.8

Example 10—ASTM F90 L-605 Alloy with Volumetric Substitution of Nickelwith Ruthenium

Element Volume Percent Weight Percent Cobalt 51.6 48.2 Chromium 25.219.3 Tungsten 7.1 14.5 Ruthenium 10.2 13.2 Manganese (maximum) 2.4 1.9Iron (maximum) 3.5 2.9

Example 11—ASTM F90 L-605 Alloy with Atomic Substitution of Nickel withOsmium

Element Atomic Percent Weight Percent Cobalt 53.9 40.8 Chromium 24.416.3 Tungsten 5.2 12.3 Osmium 10.8 26.5 Manganese (maximum) 2.3 1.6 Iron(maximum) 3.4 2.5

Example 12—ASTM F90 L-605 Alloy with Volumetric Substitution of Nickelwith Osmium

Element Volume Percent Weight Percent Cobalt 51.6 43.3 Chromium 25.217.3 Tungsten 7.1 13.0 Osmium 10.2 22.0 Manganese (maximum) 2.4 1.7 Iron(maximum) 3.5 2.6

Although Examples 1-12 illustrate complete substitution of the nickelwith a platinum group metal, it will be understood that in otherembodiments, a small fraction (e.g., about 2% by weight or less) ofnickel may remain within the modified alloy. Platinum or palladiumsubstitution is particularly preferred, as these are Group 10 elements,as is nickel. As such, these substitutions would be expected to be themost metallurgically neutral and compatible so as to maintain thestrength, ductility, and microstructural integrity (e.g., avoiding phaseseparations) of the resulting alloy. Group 9 elements (i.e., rhodium oriridium) and Group 8 elements (ruthenium or osmium) may be less likelyto substitute metallurgically neutrally for nickel. For example,ruthenium and osmium may decrease the ductility of the alloy. Thus,while such alloys are within the scope of the present disclosure, theGroup 9 elements may be more preferred and the Group 10 elements may bemost preferred. In another embodiment, one or more Group 11 elements(i.e., silver or gold) may be substituted for the nickel. In addition,although described as substituting a single platinum group metal for thenickel, it will be understood that combinations of two or more platinumgroup metals (e.g., platinum and palladium) may be used.

Further examples may be envisioned with the ASTM F90 L-605 alloy wherethe nickel, iron, and manganese have been replaced either completely orpartially with palladium, platinum, and/or other Group 8, 9, 10, or 11elements prior to melting, either singly or in combination with oneanother. Further examples may be envisioned where at least a portion ofthe cobalt is replaced by one or more elements from groups 8, 9, 10, or11 of the periodic table.

TABLE 2 ASTM F1058 Alloy Element Weight Percent Atomic Percent VolumePercent Cobalt 40 39.6 37.9 Chromium 20 22.4 23.2 Iron 16 16.7 16.9Manganese 2 2.1 2.2 Molybdenum 7 4.3 5.7 Nickel 15 14.9 14.1

As with Examples 1-12, Examples 13-16 below based on the F1058 Alloy ofTable 2 are representative examples in which the nickel has beenreplaced either volumetrically-based or atomically-based with palladiumor platinum. As with the ASTM F90 L-605 alloy, substitutions may occurfrom Group 8, 9, 10, and/or 11 elements. Trace metal elements such asberyllium, boron, carbon, phosphorus, silicon, and sulfur are notlisted.

Example 13—ASTM F1058 Alloy with Atomic Substitution of Nickel withPlatinum

Element Weight Percent Atomic Percent Cobalt 29.7 39.6 Chromium 14.822.4 Iron 11.9 16.7 Manganese 1.5 2.1 Molybdenum 5.2 4.3 Platinum 37.014.9

Example 14—ASTM F1058 Alloy with Volumetric Substitution of Nickel withPlatinum

Element Weight Percent Volume Percent Cobalt 33 37.9 Chromium 16.5 23.2Iron 13.2 16.9 Manganese 1.7 2.2 Molybdenum 5.8 5.7 Platinum 29.8 14.1

Example 15—ASTM F1058 Alloy with Atomic Substitution of Nickel withPalladium

Element Weight Percent Atomic Percent Cobalt 35.7 39.6 Chromium 17.822.4 Iron 14.2 16.7 Manganese 1.8 2.1 Molybdenum 6.3 4.3 Palladium 24.214.9

Example 16—ASTM F1058 Alloy with Volumetric Substitution of Nickel withPalladium

Element Weight Percent Volume Percent Cobalt 38.0 37.9 Chromium 19.023.2 Iron 15.3 16.9 Manganese 1.9 2.2 Molybdenum 6.7 5.7 Palladium 19.114.1

Examples 17-20 below are based on the ASTM F1058 Alloy of Table 2 inwhich the nickel, iron, and manganese have been replaced with palladiumor platinum on either an atomic or volumetric basis. These examples maybe further extended to substitution with Group 8, 9, 10, and/or 11elements. Even further examples may be envisioned where at least part ofthe cobalt is substituted by one or more elements from groups 8, 9, 10,and/or 11 of the periodic table.

Example 17—ASTM F1058 Alloy with Atomic Substitution of Nickel, Iron,and Manganese with Platinum

Element Weight Percent Atomic Percent Cobalt 22.3 39.6 Chromium 11.122.4 Molybdenum 3.9 4.3 Platinum 62.7 33.7

Example 18—ASTM F1058 Alloy with Volumetric Substitution of Nickel,Iron, and Manganese with Platinum

Element Weight Percent Volume Percent Cobalt 26.2 37.9 Chromium 13.123.2 Molybdenum 4.6 5.7 Platinum 56.1 33.2

Example 19—ASTM F1058 Alloy with Atomic Substitution of Nickel, Iron,and Manganese with Palladium

Element Weight Percent Atomic Percent Cobalt 31.1 39.6 Chromium 15.522.4 Molybdenum 5.5 4.3 Palladium 47.9 33.7

Example 20—ASTM F1058 Alloy with Volumetric Substitution of Nickel,Iron, and Manganese with Palladium

Element Weight Percent Volume Percent Cobalt 34.9 37.9 Chromium 17.423.2 Molybdenum 6.1 5.7 Palladium 41.6 33.2

TABLE 3 ASTM F562 MP-35N Alloy Element Weight Percent Atomic PercentVolume Percent Chromium 20 22.9 23.8 Nickel 35 35.5 33.7 Molybdenum 106.2 8.4 Cobalt 35 35.4 34.1

Examples 21-24 below are based on the MP-35N Alloy of Table 3 in whichthe nickel, as well as iron and titanium (present in MP-35N in smallamounts) have been replaced with palladium or platinum on an atomic orvolumetric basis. Trace elements such as beryllium, boron, carbon, iron,manganese, phosphorus, silicon, sulfur, and titanium are not listed.Further examples are envisioned where elements from groups 8, 9, 10,and/or 11 of the periodic table may be substituted for only the nickel,or also for at least some of the cobalt.

Example 21—ASTM F562 Alloy with Atomic Substitution of Nickel, Iron, andTitanium with Platinum

Element Weight Percent Atomic Percent Chromium 11 22.9 Platinum 64.235.5 Molybdenum 5.5 6.2 Cobalt 19.3 35.4

Example 22—ASTM F562 Alloy with Volumetric Substitution of Nickel, Iron,and Titanium with Platinum

Element Weight Percent Volume Percent Chromium 13.4 23.8 Platinum 56.533.7 Molybdenum 6.7 8.4 Cobalt 23.4 34.1

Example 23—ASTM F562 Alloy with Atomic Substitution of Nickel, Iron, andTitanium with Palladium

Element Weight Percent Atomic Percent Chromium 15.6 22.9 Palladium 49.435.5 Molybdenum 7.8 6.2 Cobalt 27.2 35.4

Example 24—ASTM F562 Alloy with Volumetric Substitution of Nickel, Iron,and Titanium with Palladium

Element Weight Percent Volume Percent Chromium 17.8 23.8 Palladium 42.133.7 Molybdenum 8.9 8.4 Cobalt 31.2 34.1

Relative radiopacity (RR) is a comparative measurement useful incomparing the relative radiopacity of various alloy materials. Thehigher the RR value, the greater the material's radiopacity. Forexample, 316L stainless steel has a RR value of about 2.5 barnes/cc. TheRR values for Examples 1-24, as well as the materials in Tables 1-3 areshown in Table 4 below. As can be seen, the presently disclosed alloysexhibit significantly higher relative radiopacity values than L-605,Elgiloy, or MP-35N alloys. For further comparison purposes, ASTM F138316L stainless steel has a relative radiopacity of 2.5 barnes/cc.

TABLE 4 Relative Radiopacities Example Relative Radiopacity (barnes/cc)Table 1 (ASTM F90 L-605 Alloy) 3.6 Table 2 (ASTM F1058 Elgiloy Alloy)3.1 Table 3 (ASTM F562 MP-35N Alloy) 3.5 Example 1 6.2 Example 2 5.5Example 3 5.3 Example 4 4.9 Example 5 5.2 Example 6 4.9 Example 7 6.1Example 8 5.6 Example 9 5.0 Example 10 4.8 Example 11 5.9 Example 12 5.4Example 13 6.5 Example 14 5.7 Example 15 5.4 Example 16 4.9 Example 1710.7 Example 18 9.5 Example 19 8.3 Example 20 7.5 Example 21 11.1Example 22 9.8 Example 23 8.7 Example 24 7.8

In one embodiment, any of the contemplated cobalt-based alloys may beformed by beginning with a cobalt-based alloy that does not contain theplatinum group metal (e.g., L-605, Elgiloy, Phynox, or MP-35N), butcontains another component (e.g., nickel) to be partially or completelysubstituted with the platinum group metal. The substitution may be madeby arc or otherwise melting the alloy in the presence of thesubstituting element(s) or by combining material constituents and thenmelting. The material constituents may be provided as solid pieces ofconstituent elements, powder compacts, loose powders, etc. Nickelinitially present within such a cobalt-based alloy may thus be partiallyor completely substituted with a platinum group metal prior to melting(e.g., rather than including nickel, one would include the substitutedelement). All ingredients would then be melted together to produce aningot which is then processed by conventional metalworking techniques toproduce tubing or other desired forms. The above examples illustratefinal compositions for complete substitution of the nickel, but shouldnot be construed as the sole embodiments of the invention.

In another embodiment, powdered elements of the various constituents ofthe alloy may be mixed together and then compacted and sintered so as toform the desired alloy by means of conventional powder metallurgyprocessing techniques. Other suitable alloy forming techniques may beapparent to those of skill in the art in light of the presentdisclosure.

As is apparent from the various examples, the alloys may be patternedafter an existing alloy (e.g., ASTM F90 L-605, ASTM F1058 Elgiloy orPhynox, or ASTM F562 MP-35N) in which at least the nickel and optionallythe iron, manganese and/or other constituents have been substituted witha platinum group metal. The substitution may proceed so as to maintainthe atomic percentage of the original composition, or alternatively, thevolume percentage of the original composition. Another embodiment mayinclude weight percentage substitution with the platinum group metal. Inother embodiments, as described herein, the nickel may not be replaced,and tungsten may be increased beyond its solubility limit (e.g., seeExamples 133-136).

As described above, according to an alternative embodiment, the alloysmay be similar to those described above in which at least the nickel hasbeen substituted with a platinum group metal, but in which thesubstituting metal is a refractory metal selected from the groupconsisting of silver, gold, hafnium, niobium, rhenium, tantalum,molybdenum, tungsten, zirconium, or combinations thereof. It is alsoconceivable that the substituting elements may be a combination ofplatinum group metals and refractory metals.

As described above, substitution may be on an atomic basis, a volumetricbasis, or a weight basis. Examples 25-69 below are based on weightpercentage substitution of at least the nickel of an L-605 alloy and anMP-35N alloy. It will be understood that additional examples maysubstitute at least the nickel (and preferably at least some of theiron) of other cobalt-chromium alloys such as Elgiloy or Phynox.Additionally, it will be understood that substitution may alternativelyproceed on an atomic or volumetric basis.

In order to better understand Examples 25-69, the various binary phasediagrams of the included elements will be discussed.

When considering the cobalt-chromium alloy systems from the perspectiveof elimination of nickel from the alloys, substitution of anotherelement for the nickel in the alloy is a natural approach. Whenconsidering which elements to utilize for substitution, the desired endgoals come into play. The goal of such substitution is to create analloy that has a greater radiopacity than the unmodified alloy (e.g.,L-605 or MP-35N). In order to create an alloy with greater radiopacity,one or more elements of higher atomic weight and greater relativeradiopacity (RR) need to be utilized.

In reviewing the periodic table of the elements, and the binary phasediagrams for the heavier transition metal and other precious metalelements in the periodic table, a number of elements stand out asappropriate for the substitution of nickel. Further substitution forsome of the cobalt in the alloy(s) is possible with the desire for evenbetter radiopacity of the alloy compared to L-605 and MP-35N. Theseelements include refractory metal elements such as Zr, Nb, Mo, Hf, Ta,W, and Re, and precious metal elements such as Ag and Au (which areherein grouped with the refractory elements for sake of simplicity).

To understand the reasoning behind these selections, the phase diagramsfor the L-605 CoCr (Co-20Cr-15W-10Ni) and MP-35N (35Co-35Ni-20Cr-10Mo)alloys are first discussed below. When reviewing these phase diagramsthey appear complex. The following points, however, work in favor ofhaving alloys that have properties that allow them to be mechanicallyworked into a variety of useful forms, including stent tubing. For easeof understanding, elements less than 5 weight percent (e.g., manganese,iron, etc.) are ignored in this analysis, and presumed to be part of thecobalt concentration.

For the most part, the discussion will be limited to phases that arepredicted to exist at the temperatures of interest, which include bodytemperature and room temperature. Also, when discussing compositions,all are considered “relative” compositions to relate them to the binaryphase diagram unless otherwise indicated. For example, an alloyincluding 55 weight percent Co and 20 weight percent Cr (“55Co-20Cr”)would translate to a relative composition of 73Co-27Cr in weightpercent. All substituted alloy compositions below are discussed weightpercent, unless otherwise indicated. Phase structures discussed includebody-centered-cubic (BCC), face-centered-cubic (FCC),hexagonal-close-packed (HCP), orthorhombic, rhombohedral, tetragonal,and body-centered-tetragonal (BCT).

For L-605 CoCr:

-   -   Co—Cr is a complex phase diagram with eutectic, eutectoid,        peritectic, peritectoid, and congruent features. It includes at        least three distinct phases and two eutectoid compositions. The        tetragonal σ intermetallic peritectoid phase exists from about        51 to about 64Cr. L-605 falls into the HCP (εCo) phase area of        the diagram (FIGS. 4A-4B).    -   Co—Ni is a solid solution across the entire phase diagram, with        an atomic structure change from HCP to FCC that occurs around        25Ni. L-605 falls into the (εCo) HCP phase area of the diagram        (FIGS. 5A-5B).    -   Cr—Ni is a phase diagram with eutectic, peritectoid, and        allotropic transformation features. L-605 falls in the eutectoid        body centered cubic (BCC)-orthorhombic area of the phase diagram        (FIGS. 6A-6B).    -   Co—W is an extremely complex phase diagram with eutectic,        eutectoid, peritectoid, and allotropic transformation features.        L-605 falls within the eutectoid HCP (εCo)—BCC (W) portion of        the phase diagram (FIGS. 7A-7B).    -   Cr—W is a phase diagram with a large miscibility gap starting        around 15 weight percent W. L-605 resides in the miscibility gap        (α1+α2) with two BCC phases (FIGS. 8A-8B).    -   Ni—W is a complex phase diagram with eutectic and multiple        peritectoid reactions. L-605 falls in the eutectoid BCT        Ni4W—orthorhombic NiW phase combination (FIGS. 9A-9B).

For MP-35N CoCr:

-   -   Co—Cr—MP-35N falls into a eutectoid structure comprised of HCP        (εCo) and tetragonal σ phases (FIGS. 4A-4B).    -   Co—Ni—MP-35N falls in the FCC (αCo,Ni) portion of the phase        diagram (FIGS. 5A-5B).    -   Cr—Ni—MP-35N falls in the orthorhombic ordered phase regime of        Ni₂Cr. It is possible that the presence of the other elements        suppresses the formation of this ordered phase (FIGS. 6A-6B).    -   Co—Mo is a complex phase diagram with multiple eutectic,        peritectoid, and allotropic transformations. Similar to Co—W,        two distinct ordered phases are formed, from about 33 to about        35Mo and from about 53 to about 61Mo. MP-35N falls in the region        combining HCP κ and HCP (εCo) phases (FIGS. 10A-10B).    -   Cr—Mo exhibits a non-mixing region, called a miscibility gap,        across most of the phase diagram. This indicates that distinct        BCC phases of Cr and of Mo may exist without full mixing of the        atoms among each other. MP-35N falls within this miscibility gap        (Cr)+(Mo) region (FIGS. 11A-11B).    -   Ni—Mo is a phase diagram that exhibits eutectic, peritectoid,        and allotropic transformations. MP-35N falls in the FCC solid        solution (Ni) regime of the phase diagram (FIGS. 12A-12B).

As can be seen from the complex phase diagrams described above, theequilibrium microstructures need not be single phase (i.e., fully solidsolution) for an alloy composition to be selected that works well (as itis already established that L-605 and MP-35N work from a workabilityperspective, although with relatively lower radiopacity than desired).

The next discussion covers the elements listed above from theperspective of substituting for part or all of the Ni and possibly partof the Co in L-605 and MP-35N alloys. Other Co—Cr alloys (e.g., Elgiloy,Phynox) could similarly be substituted. In addition, an entirely newalloy composition may be developed independent of basing the initialsubstitution on existing alloys.

For an alloy containing Ag, considering different compositions that mayinclude Mo and/or W:

-   -   Ag—Co phase diagram shows a complete miscibility gap with two        allotropic transformations. Any mixture at the temperatures of        interest will simply include a mixture of FCC (Ag) and HCP (εCo)        phases (FIGS. 13A-13B).    -   Ag—Cr phase diagram shows a eutectic and a miscibility gap with        two allotropic transformations. At the temperatures of interest,        any mixture will simply include FCC (Ag) and BCC (Cr) phases        regardless of composition (FIGS. 14A-14B).    -   Ag—Mo is a phase diagram with a eutectic at the Ag side and an        allotropic transformation. With the two elements being        immiscible at the temperatures of interest, the material will        simply include a mixture of FCC (Ag) and BCC (Mo) phases        regardless of composition (FIGS. 15A-15B).    -   Ag—W is completely immiscible across all compositions. This        indicates that the material will simply include a mixture of FCC        (Ag) and BCC (W) phases.

For an alloy containing Au, considering different compositions that mayinclude Mo and/or W:

-   -   Au—Co is a phase diagram with eutectic, eutectoid, and        allotropic transformation features. The material will simply        include a mixture of FCC (Au) and HCP (εCo) phases regardless of        composition (FIGS. 16A-16B).    -   Au—Cr displays eutectic and ordering in the phase diagram. From        about 1 to 6Au, an ordered Au₄Cr (α′) BCT phase forms. Above        this region the material will include a mixture of BCT α′ and        BCC (Cr) phases (FIGS. 17A-17B).    -   Au—Mo is a eutectic across the entire phase diagram. This        indicates that the material will include a mixture of FCC (Au)        and BCC (Mo) phases regardless of composition (FIGS. 18A-18B).    -   Au—W is a eutectic across the entire phase diagram. This        indicates that the material will include a mixture of FCC (Au)        and BCC (W) phases regardless of composition (FIGS. 19A-19B).

For an alloy containing Hf, considering different compositions that mayinclude Mo and/or W:

-   -   Co—Hf is a complex phase diagram with multiple eutectics,        eutectoids, peritectics, congruent, and allotropic        transformations. It is possible that this mixture becomes        paramagnetic as early as about 47Hf. Up to this point, (e.g.,        about 46.5Hf), the microstructure will be a combination of HCP        (εCo) and tetragonal Co₇Hf₂. From about 46.5 to about 56Hf, the        microstructure is a mix of tetragonal Co₇Hf₂ and FCC Co₂Hf. From        about 56 to about 62.5Hf is the ordered FCC Co₂Hf phase. From        about 62.5 to about 74.5Hf the microstructure is a mixture of        FCC Co₂Hf and cubic CoHf phases. The cubic CoHf phase sits from        about 74.5 to about 75.5Hf. From about 75.5 to about 86Hf, the        microstructure is a mix of the cubic CoHf and FCC CoHf₂ phases.        The FCC CoHf₂ phase sits from about 86 to about 89Hf. Above        about 89Hf is a mixture of FCC CoHf₂ and HCP (αHf) phases (FIGS.        20A-20B).    -   Cr—Hf phase diagram shows two eutectics, one eutectoid, and one        intermediate FCC Cr₂Hf phase from about 62 to about 65Hf. Below        this intermediate phase the microstructure should include FCC        Cr₂Hf plus (Cr) BCC phases. Above the Cr₂Hf phase, the eutectic        should be a mix of Cr₂Hf and HCP (αHf) phases (FIGS. 21A-21B).    -   Hf—Mo is a complex phase diagram with eutectic, eutectoid,        peritectic, and allotropic phase transformations. Only one        ordered FCC αMo₂Hf phase exists at the temperatures of interest,        from about 47 to about 50 relative weight percent Hf. Up to        about 25Hf, a BCC (Mo) solid solution exists. From about 25 to        about 47Hf the microstructure would be a mix of BCC (Mo) solid        solution and FCC αMo₂Hf. Above about 50Hf is a mix of this phase        (i.e., FCC αMo₂Hf) and HCP (αHf) (FIGS. 22A-22B).    -   Hf—W, similar to Hf—Mo, is a phase diagram with a eutectic,        eutectoid, peritectic/ordered phase, with allotropic        transformations. The one ordered FCC HfW₂ phase exists from        about 66 to about 68Hf. Below this phase the microstructure is a        mix of BCC (W) and FCC HfW₂. Above this phase is a mix of FCC        HfW₂ and HCP (αHf) (FIGS. 23A-23B).

For an alloy containing Mo, the following may be observed:

-   -   Co—Mo is a complex phase diagram with two eutectics, a        peritectic, peritectoids/ordered phases, and allotropic        transformations. Two distinct ordered phases exist at the        temperature of interest. The HCP κ phase falls from about 34 to        about 36Mo while the rhombohedral ε phase falls from about 53 to        about 61Mo. Up to about 6Mo, HCP (εCo) appears to be the primary        phase. From about 6 to about 34Mo is an HCP (εCo) and HCP κ        mixture. From about 36 to about 53Mo a mixture of HCP κ and        rhombohedral e exist. Above about 61Mo is a mixture of        rhombohedral c and BCC (Mo) (FIGS. 24A-24B).    -   Cr—Mo phase diagram exhibits a miscibility gap from about 9Mo        through about 95Mo. Based on the shape of the miscibility curve        at 500° C., it is likely that this extends to close to 2Mo        through 99+Mo at room/body temperature. This indicates that the        microstructure will be a mixture of (Cr)+(Mo) BCC phases (FIGS.        25A-25B).    -   Mo—W phase diagram exhibits a continuous BCC solid solution        (Mo,W) regardless of composition (FIGS. 26A-26B).

For an alloy containing Nb, considering different compositions that mayinclude Mo and/or W′:

-   -   Co—Nb is a complex phase diagram with multiple eutectics and        congruent ordered phases, including one phase specific to a        single composition. These phases include an HCP NbCo₃ phase at        about 34.5Nb, an FCC αNbCo₂ phase from about 37 to about 44Nb,        and rhombohedral Nb₆Co₇ from about 61 to about 64Nb. Up to about        34.5Nb most likely is a mixture of HCP (εCo) and HCP NbCo₃. From        about 34.5 to about 37Nb is a mixture of HCP NbCo₃ and FCC        αNbCo₂ phases. From about 44 to about 61Nb is a mixture of FCC        αNbCo₂ and rhombohedral Nb₆Co₇. Above about 64Nb is a mixture of        rhombohedral Nb₆Co₇ and BCC (Nb) phases (FIGS. 27A-27B).    -   Cr—Nb shows two eutectics and a congruent ordered phase around        the middle of the phase diagram. The ordered FCC Cr₂Nb phase        falls from about 47 to about 52Nb. Up to about 47Nb exists a mix        of BCC (Cr) and FCC Cr₂Nb phases. Above about 52Nb exists a mix        of FCC Cr₂Nb and BCC (Nb) phases (FIGS. 28A-28B).    -   Mo—Nb phase diagram shows a single solid solution BCC (Mo,Nb)        phase across the entire range of compositions (FIGS. 29A-29B).    -   Nb—W phase diagram shows a single solid solution BCC (Nb,W)        phase across the entire range of compositions (FIGS. 30A-30B).

For an alloy containing Re, considering different compositions that mayinclude Mo and/or W:

-   -   Co—Re forms an HCP solid solution phase of (εCo, Re) across the        entire phase diagram at the temperatures of interest (FIGS.        31A-31B).    -   Cr—Re is a phase diagram with eutectic and peritectic reactions.        Up to about 66Re the microstructure is primarily BCC (Cr). From        about 66 to about 83Re is a mixture of BCC (Cr) and σ phases. A        tetragonal ordered phase (the σ phase, also written as Cr₂Re₃)        forms from about 83 to about 88Re. Above about 88Re through        about 97Re, a mixture of a and HCP (Re) phases exist. Above        about 97Re, the dominant microstructure is HCP (Re) (FIGS.        32A-32B).    -   Mo—Re phase diagram is a combination of a eutectic, congruent,        peritectoid, and allotropic phase transformation. Up to about        38Re a BCC (Mo) solid solution phase exists. From about 28Re to        about 86Re is a mix of BCC (Mo) and BCC χ phases. From about 86        to about 88Re is the ordered BCC χ phase. From about 88 to about        95.5Re a combination of BCC χ and HCP (Re) phases exist. Above        about 96 relative weight percent the structure is a solid        solution HCP (Re) phase (FIGS. 33A-33B).    -   Re—W is a complex phase diagram with eutectic, peritectoid, and        congruent features. Up to about 28Re is a solid solution BCC (W)        phase. From about 28 to about 44Re is a combination of BCC (W)        and tetragonal σ phases. From about 44 to about 64Re is the        ordered tetragonal σ phase. From about 64 to about 72Re is a        combination of tetragonal σ and BCC χ phases. From about 72 to        about 74Re is the ordered BCC χ phase. From about 74 to about        88Re is a combination of BCC χ and HCP (Re) phases. Above about        88Re, a HCP solid solution phase with W exists (FIGS. 34A-34B).

For an alloy containing Ta, considering different compositions that mayinclude Mo and/or W:

-   -   Co—Ta is a fairly complex phase diagram that exhibits five        ordered phases, three of which are peritectic. Up to about 3Ta        is HCP (εCo). From about 3 to about 46.5Ta is a mixture of HCP        (εCo) and Co₇Ta₂ (unknown microstructure). The Co₇Ta₂ phase sits        at about 46.5Ta. From about 46.5 to about 54Ta is a combination        of Co₇Ta₂ and HCP λ₃ phases. The HCP λ₃ phase sits from about 54        to about 55.5Ta. From about 55.5 to 57Ta is a mixture of HCP λ₃        and FCC Co₂Ta (λ₂) phases. From about 57 to about 63Ta is the        FCC Co₂Ta (λ₂) phase. From about 63 to about 70.5Ta is mixture        of FCC Co₂Ta (λ₂) and rhombohedral Co₆Ta₇ phases. From about        70.5 to 79.5Ta is the Co₆Ta₇ rhombohedral phase. From about 79.5        to about 86Ta is a mixture of rhombohedral Co₆Ta₇ and BCT CoTa₂        phases. A BCT CoTa₂ phase sits at around 86Ta. Above about 85Ta        is a mixture of BCT CoTa₂ and BCC (Ta) phases (FIGS. 35A-35B).    -   Cr—Ta is a phase diagram with a single intermediate phase that        forms a eutectic with each of the (Cr) and (Ta) solid solutions.        The intermediate Laves phase formation of FCC Cr₂Ta sits from        about 63 to about 66.5Ta. Up to about 63Ta, the microstructure        is a mixture of BCC (Cr) and FCC Cr₂Ta. Above about 66.5Ta is a        mixture of FCC Cr₂Ta and BCC (Ta) (FIGS. 36A-36B).    -   Mo—Ta forms a continuous BCC (Mo,Ta) solid solution at all        compositions (FIGS. 37A-37B).    -   Ta—W forms a continuous BCC (Ta,W) solid solution at all        compositions (FIGS. 38A-38B).

For an alloy containing W, the following may be observed:

-   -   Co—W is an extremely complex phase diagram with eutectic,        eutectoid, peritectoid, and allotropic transformations featuring        two different ordered phases at the temperatures of interest.        HCP Co₃W forms from about 48 to about 51.5W. Rhombohedral Co₇W₆        forms from about 70 to about 74.5W. Up to about 48W the        microstructure is a mixture of HCP (εCo) and HCP Co₃W phases.        From about 51.5 to about 70W, the microstructure is a mixture of        HCP Co₃W and rhombohedral Co₇W₆ phases. Above about 74.5W is a        mixture of rhombohedral Co₇W₆ and BCC (W) phases. Based on the        L-605 information and the similar MP-35N Co—Mo information,        alloys that fall outside of the ordered phases allow for a        workable alloy (FIGS. 39A-39B).    -   Cr—W is a phase diagram with a large miscibility gap starting        around 15 weight percent W. Note that the miscibility gap most        likely starts closer to 0-1W at the temperatures of interest,        based on the shape of the curve. Below the start of the        miscibility gap is a solid solution of BCC (Cr,W). Within the        miscibility gap the two BCC (α₁+α₂) Cr and W phases exist (FIGS.        40A-40B).    -   Mo—W forms a continuous BCC (Mo,W) solid solution at all        compositions (FIGS. 41A-41B).

For an alloy containing Zr, the following may be observed:

-   -   Co—Zr is a complex phase diagram with eutectic, eutectoid,        peritectic, and allotropic transformations. The formation of        five different ordered phases are shown. The γ phase, of unknown        structure, is at about 22Zr. The FCC δ phase appears at about        28Zr. The FCC ε phase appears roughly from about 39 to about        45Zr. The cubic ζ phase appears at about 61Zr. The BCT η phase        appears at about 75.5Zr. Up to about 22Zr, the microstructure is        a combination of HCP (εCo) and FCC γ phases. From about 22 to        about 28Zr is a mixture of FCC γ and FCC δ phases. From about 28        to about 39Zr is a mixture of FCC δ and FCC ε phases. From about        45 to about 61Zr is a mixture of FCC ε and cubic ζ phases. From        about 61 to about 75.5Zr is a mixture of cubic ζ and BCT η        phases. From about 75.5 to about 99Zr is a mixture of BCT η        phase and HCP (αZr) phases. Above 99Zr is a solid solution HCP        (αZr) phase (FIGS. 42A-42B).    -   Cr—Zr is a complex phase diagram with eutectic, eutectoid,        congruent and allotropic transformation features. One        intermediate ordered phase exists at the temperature of        interest. That FCC αZrCr₂ phase falls from about 44 to about        50Zr. Up to about 44Zr is a combination of BCC (Cr) and FCC        αZrCr₂ phases. Above about 50Zr is a combination of FCC αZrCr₂        and HCP (αZr) phases (FIGS. 43A-43B).    -   Mo—Zr is a phase diagram with eutectic, peritectic, eutectoid,        and allotropic transformation features. A single ordered FCC        Mo₂Zr phase exists from about 32 to about 39Zr. Up to about 32Zr        is a mixture of BCC (Mo) and FCC Mo₂Zr phases. Above about 39Zr        is a mixture of FCC Mo₂Zr and HCP (αZr) phases (FIGS. 44A-44B).    -   W—Zr is a phase diagram with eutectic features, showing a single        ordered FCC W₂Zr phase at around 20Zr. Up to about 20Zr is a        mixture of BCC (W) and FCC W₂Zr phases. Above about 20Zr is a        mixture of FCC W₂Zr and HCP (αZr) phases (FIGS. 45A-45B).

For an alloy containing Co, Cr, Fe and Pd or Pt (e.g., as discussed inmore detail in conjunction with Examples 78-89, and particularly Example85, below), the following may be observed:

-   -   Co—Fe is a phase diagram showing a miscibility gap between about        28 and about 74Fe, with a basic cubic structure of the two        intermixed Co and Fe phases. Above and below these compositions        the structure is a solid solution Co and Fe mixture with a BCC        structure (FIGS. 46A-46B).    -   Co—Pd phase diagram shows a continuous solid solution with an        HCP (εCo) structure (FIGS. 47A-47B).    -   Co—Pt phase diagram shows a solid solution structure with two        miscibility gaps and two focal phase formations. Up to about        69Pt the structure is HCP (εCo) and FCC α(Co,Pt). Between about        69 and about 91Pt there is a miscibility gap, with a focal        tetragonal CoPt structure at about 76Pt. Above 91Pt there is        again FCC α(Co,Pt) (FIGS. 48A-48B).    -   Cr—Fe is a somewhat complex phase diagram with a variety of        features. This system displays a BCC eutectic structure between        about 3 and about 97Fe. Above 97Fe, the structure is primarily        FCC, while below 3Fe the structure is primarily BCC (FIGS.        49A-49B).    -   Cr—Pd is a fairly complex phase diagram. Up to about 67Pd, the        structure is a mixture of FCC (Cr) and tetragonal CrPd. Between        about 67 and about 69Pd the structure is tetragonal CrPd.        Between about 69 and about 71Pd, the structure is a mixture of        tetragonal CrPd and FCC Cr₂Pd₃. Between about 71 and about 88Pd        the structure is FCC Cr₂Pd₃. Above about 88Pd, the structure is        FCC (Pd) (FIGS. 50A-50B).    -   Cr—Pt is a fairly complex phase diagram. Up to about 5Pt, the        structure is FCC (Cr). From about 5 to about 43Pt the structure        is a mix of FCC (Cr) and cubic Cr₃Pt. From about 43 to about        51Pt the structure is cubic Cr₃Pt. From about 51 to about 78Pt        the structure is a mix of cubic Cr₃Pt and tetragonal CrPt. From        about 78 to about 80Pt the structure is tetragonal CrPt. From        about 80 to about 96Pt the structure is primarily cubic CrPt₃.        Above about 96Pt the structure is FCC (Pt) (FIGS. 51A-51B).    -   Fe—Pd is a complex phase diagram. Up to about 65Pd is a        combination of FCC (γFe,Pd) and tetragonal FePd. From about 65        to about 75Pd is tetragonal FePd. From about 75 to about 93Pd is        cubic FePd₃. Above around 93Pd is FCC (γFe,Pd) (FIGS. 52A-52B).    -   Fe—Pt phase diagram shows a eutectic with multiple intermediate        phases. Up to about 18Pt is a BCC solid solution. Between about        18 and about 38Pt is an FCC solid solution. Between about 38 and        about 62Pt is cubic γ₁ (Fe₃Pt). Between about 63 and about 82Pt        is tetragonal 72 (FePt). Between about 82 and about 94Pt is        cubic γ₃ (FePt₃). Above about 94Pt, the structure is a        continuous solid solution with a FCC structure (FIGS. 53A-53B).    -   Pd—Pt phase diagram shows a continuous solid solution that is a        mixture of FCC (Pd)+(Pt) across the majority of compositions. At        some undefined lower and upper compositions the phase is        primarily FCC (Pd) or FCC (Pt) (FIGS. 54A-54B).

In considering the possible alloys from both a radiopacity and acompatibility perspective, the following possible compositions come tothe forefront. Note that minor and trace elements are not considered inthese calculations. It is important to avoid the Co—Cr σ intermetallicphase, because this phase is quite brittle. The examples below willexplicitly discuss avoidance of this phase by remaining below the 51-64weight percent Cr in the Co—Cr regime. It is also envisioned that viablealloy compositions may be provided above this regime (i.e., greater thanabout 64Cr in the Co—Cr regime) that would provide workable alloys. Forexample, 10Co and 20Cr would give a relative composition of 33.3Co and66.7Cr, moving above the σ intermetallic regime.

Examples 25-30 below are based on the nominal compositions of the ASTMF90 L-605 Alloy of Table 1 and the ASTM F562 MP-35N Alloy of Table 3 inwhich at least the nickel, and in some examples, some of the cobalt hasbeen replaced on an weight substitution basis with a refractory metal,silver. Example 31 further replaces the tungsten of L-605 or themolybdenum of MP-35N with silver so that the alloy is essentially aternary Co—Cr—Ag alloy. Trace elements such as beryllium, boron, carbon,iron, manganese, phosphorus, silicon, sulfur, and titanium are notlisted.

Example 25—ASTM F90 L-605 Alloy with Weight Substitution of Nickel withSilver

Element Weight Percent Cobalt 55 Chromium 20 Tungsten 15 Silver 10

From a metallurgical perspective, the Co—Cr, Co—W, and Cr—W will fall inthe same regions as for L-605. Otherwise the alloy will also include aseries of eutectic immiscible phases of FCC Ag, HCP εCo, BCC Cr, and BCCW. This alloy would otherwise behave similarly to L-605, but withincreased relatively radiopacity (to about 4.7 barnes/cc).

Example 26—ASTM F90 L-605 Alloy with Weight Substitution of Nickel and aPortion of the Cobalt with Silver

Element Weight Percent Cobalt 35 Chromium 20 Tungsten 15 Silver 30

In order to increase the radiopacity, the silver may be increased(beyond simply substituting for Ni) to also substitute for a portion ofthe cobalt. For example, increasing the silver to 30 weight percentwould lower cobalt to 35 weight percent, leaving the other elements thesame. This results in a calculated radiopacity of 7.0 barnes/cc. Similarto Example 25, the silver would result in a series of immiscible phaseswith Co, Cr, and W. Co—Cr would shift to be in the same region asMP-35N. Co—W would shift higher but still remain in the same phaseregion as L-605. Cr—W would remain the same as L-605. This would resultin a workable alloy.

Example 27—ASTM F90 L-605 Alloy with Weight Substitution of Nickel and aPortion of the Cobalt with Silver

Element Weight Percent Cobalt 25 Chromium 20 Tungsten 15 Silver 40

If even higher radiopacity is desired, the silver may be increased to 40weight percent. This results in a calculated radiopacity of 8.2barnes/cc. Similar to Example 26, the silver would remain a series ofimmiscible phases with Co, Cr, and W. Co—Cr would shift to be in thesame region as MP-35N, closer to the middle of the phase. Co—W shiftshigher but remains in the same phase region as L-605. Cr—W would remainthe same as for L-605. This would result in a workable alloy.

Example 28—ASTM F90 L-605 Alloy with Weight Substitution of Nickel and aPortion of the Cobalt with Silver

Element Weight Percent Cobalt at least 20 Chromium 20 Tungsten 15 Silverup to 45

Assuming that Cr and W are not changed, Ag should remain at or belowabout 45 weight percent (e.g., 10 to 45 weight percent) in order toavoid the Co—Cr a intermetallic phase. At 45 weight percent Ag,calculated radiopacity would be 8.8 barnes/cc.

Example 29—ASTM F562 MP-35N Alloy with Weight Substitution of Nickelwith Silver

Element Weight Percent Cobalt 35 Chromium 20 Molybdenum 10 Silver 35

Utilizing a straight substitution of silver for nickel on a weightpercentage basis results in the calculated radiopacity increasing from3.4 barnes/cc to 7.0 barnes/cc. From a metallurgical perspective, thealloy includes a series of eutectic immiscible phases of FCC Ag, HCPεCo, BCC Cr, and BCC Mo with Co—Cr, Co—Mo, and Cr—Mo falling in the sameregions as MP-35N. This alloy would otherwise behave similarly toMP-35N, but with increased relatively radiopacity (to about 7.0barnes/cc).

Example 30—ASTM F562 MP-35N Alloy with Weight Substitution of Nickel anda Portion of the Cobalt with Silver

Element Weight Percent Cobalt at least 20 Chromium 20 Molybdenum 10Silver up to 50

Assuming that Cr and Mo are not changed, Ag should remain at or belowabout 50 weight percent (e.g., 35 to 50 weight percent) in order toavoid the Co—Cr a intermetallic phase. At 50 weight percent Ag,calculated radiopacity would be 8.7 barnes/cc.

Example 31—ASTM F90 L-605 Alloy or ASTM F562 MP-35N Alloy with WeightSubstitution of Nickel and Tungsten or Molybdenum with Silver

Element Weight Percent Cobalt at least 20 Chromium 20 Silver up to 60

When considering the disparity in melting temperature between Ag and Moand W, the alloy may be considered without either of these elements (theMo or W), i.e., consisting of Ag—Co—Cr only. In this instance, the Agmay range up to about 60 weight percent to avoid the Co—Cr σintermetallic phase. At 60 weight percent Ag, calculated radiopacitywould be 9.0 barnes/cc. Ag—Co and Ag—Cr both fall into the eutecticregimes of these phase diagrams.

Examples 32-35 below are based on the nominal compositions of the ASTMF90 L-605 Alloy of Table 1 and the ASTM F562 MP-35N Alloy of Table 3 inwhich at least the nickel, and in some examples, some of the cobalt hasbeen replaced on an weight substitution basis with a refractory metal,gold. Example 36 further replaces the tungsten of L-605 or themolybdenum of MP-35N with gold so that the alloy is essentially aternary Co—Cr—Au alloy. Trace elements such as beryllium, boron, carbon,iron, manganese, phosphorus, silicon, sulfur, and titanium are notlisted.

Example 32—ASTM F90 L-605 Alloy with Weight Substitution of Nickel withGold

Element Weight Percent Cobalt 55 Chromium 20 Tungsten 15 Gold 10

Substituting Au for Ni on a weight percentage basis increases thecalculated radiopacity from 3.6 to 4.6 barnes/cc. From a metallurgicalperspective, the Co—Cr, Co—W, and Cr—W will fall in the same regions asfor L-605. Otherwise the alloy will also include a series of eutecticimmiscible phases of FCC Au, BCC α′ and HCP εCo, BCC Cr, and BCC W. Thisalloy would otherwise behave similarly to L-605, but with increasedrelatively radiopacity (to about 4.6 barnes/cc).

Example 33—ASTM F90 L-605 Alloy with Weight Substitution of Nickel and aPortion of the Cobalt with Gold

Element Weight Percent Cobalt at least 20 Chromium 20 Tungsten 15 Goldup to 45

As with Ag, assuming that Cr and W are not changed, Au should remain ator below about 45 weight percent (e.g., 10 to 45 weight percent) inorder to avoid the Co—Cr σ intermetallic phase. At 45 weight percent Au,calculated radiopacity would be 8.9 barnes/cc.

Example 34—ASTM F562 MP-35N Alloy with Weight Substitution of Nickelwith Gold

Element Weight Percent Cobalt 35 Chromium 20 Molybdenum 10 Gold 35

Utilizing a straight substitution of gold for nickel on a weightpercentage basis results in the calculated radiopacity increasing from3.4 barnes/cc to 6.8 barnes/cc. From a metallurgical perspective, thealloy includes a series of eutectic immiscible phases of FCC Au, BCC α′and HCP εCo, BCC Cr, and BCC Mo with Co—Cr, Co—Mo, and Cr—Mo falling inthe same regions as MP-35N. Similar to the MP-35N alloy, this wouldresult in a workable alloy.

Example 35—ASTM F562 MP-35N Alloy with Weight Substitution of Nickel anda Portion of the Cobalt with Gold

Element Weight Percent Cobalt at least 20 Chromium 20 Molybdenum 10 Goldup to 50

Assuming that Cr and Mo are not changed, Au should remain at or belowabout 50 weight percent (e.g., 35 to 50 weight percent) in order toavoid the Co—Cr a intermetallic phase. At 50 weight percent Au,calculated radiopacity would be 8.7 barnes/cc.

Example 36—ASTM F90 L-605 Alloy or ASTM F562 MP-35N Alloy with WeightSubstitution of Nickel and Tungsten or Molybdenum with Gold

Element Weight Percent Cobalt at least 20 Chromium 20 Gold up to 60

When considering the disparity in melting temperature between Au and Moand W, the alloy may be considered without either of these elements (theMo or W), i.e., consisting of Au—Co—Cr only. In this instance, the Aumay range up to about 60 weight percent to avoid the Co—Cr σintermetallic phase. At 60 weight percent Au, calculated radiopacitywould be 9.2 barnes/cc. Au—Co and Au—Cr both fall into the eutecticregimes of these phase diagrams.

Examples 37-40 below are based on the nominal compositions of the ASTMF90 L-605 Alloy of Table 1 and the ASTM F562 MP-35N Alloy of Table 3 inwhich at least the nickel, and in some examples, some of the cobalt hasbeen replaced on an weight substitution basis with a refractory metal,hafnium. Example 41 further replaces the tungsten of L-605 or themolybdenum of MP-35N with hafnium so that the alloy is essentially aternary Co—Cr—Hf alloy. Trace elements such as beryllium, boron, carbon,iron, manganese, phosphorus, silicon, sulfur, and titanium are notlisted.

When considering such systems, a few items should be taken into account.As Hf falls in the refractory metal category and L-605 and MP-35N Coalloys already include tungsten or Mo, respectively, which also fallinto this category, the metallurgical behavior of Hf may be inferredfrom Co—Mo and Co—W phase diagrams. It is noted that Hf has a largeeffect on other refractory metals and on Ni and Fe based alloys in smallamounts. The grain boundary pinning effect that is experienced insmaller additions will not continue with larger additions. Furthermore,the Co—Hf mixture may be partially paramagnetic as early as around 47weight percent Hf. As with other alloys, it is likely that this behavioris repressed by the other elements in the alloy, resulting in a workablealloy.

Example 37—ASTM F90 L-605 Alloy with Weight Substitution of Nickel withHafnium

Element Weight Percent Cobalt 55 Chromium 20 Tungsten 15 Hafnium 10

Substituting Hf for Ni on a weight percentage basis increases thecalculated radiopacity from 3.6 to 4.3 barnes/cc. From a metallurgicalperspective, the Co—Cr, Co—W, and Cr—W will fall in the same regions asfor L-605. For Hf—Co, the alloy will fall within the mixed HCP εCo andtetragonal Co₇Hf₂ regime. For Hf—Cr, the alloy will fall within the FCCCr₂Hf plus BCC Cr phases. For Hf—Mo the mixture would include BCC W andFCC HfW₂. It is expected that this alloy may be stronger than L-605.

Example 38—ASTM F90 L-605 Alloy with Weight Substitution of Nickel and aPortion of the Cobalt with Hafnium

Element Weight Percent Cobalt at least 20 Chromium 20 Tungsten 15Hafnium up to 45

As with Ag and Au, here it is assumed that Cr and W are not changed. Ataround 30 weight percent Hf, radiopacity would be 5.8 barnes/cc. Phaseswould include a combination of HCP εCo and tetragonal Co₇Hf₂, Cr₂Hf, HCPαHf, and FCC HfW₂. If the suppression of the paramagnetism is successfuland strengthening is not too much to allow workability, Hf may beincreased up to 45 weight percent. At 45 weight percent Hf, theradiopacity is 7.2 barnes/cc, and metallurgically would result in a mixof FCC Co₂Hf and cubic CoHf, FCC Cr₂Hf and some HCP αHf, and FCC HfW₂and HCP αHf phases.

Example 39—ASTM F562 MP-35N Alloy with Weight Substitution of Nickelwith Hafnium

Element Weight Percent Cobalt 35 Chromium 20 Molybdenum 10 Hafnium 35

Utilizing a straight substitution of hafnium for nickel on a weightpercentage basis results in the calculated radiopacity increasing from3.4 barnes/cc to 5.7 barnes/cc. From a metallurgical perspective, Co—Cr,Co—Mo, and Cr—Mo will fall in the same regions as MP-35N. Co—Hf fallsinto the possible partially paramagnetic regime with the combination oftetragonal Co₇Hf₂ and FCC Co₂Hf. Presuming the suppression of theparamagnetism by the presence of the other elements in the alloy, thisalloy would also include a combination of FCC Cr₂Hf, FCC αMo₂Hf and HCPαHf phases.

Example 40—ASTM F562 MP-35N Alloy with Weight Substitution of Nickel anda Portion of the Cobalt with Hafnium

Element Weight Percent Cobalt at least 20 Chromium 20 Molybdenum 10Hafnium up to 50

If the suppression of the paramagnetism is successful and strengtheningis not too much to still allow workability, Hf may be included up toabout 50 weight percent. This would result in a radiopacity of 6.9barnes/cc. Phases in this alloy beyond the MP-35N Co—Cr, Co—Mo and Cr—Mophase mixtures would include FCC Co₂Hf and cubic CoHf, FCC Cr₂Hf and HCPαHf, and FCC αMo₂Hf and HCP αHf phases.

Example 41—ASTM F90 L-605 Alloy or ASTM F562 MP-35N Alloy with WeightSubstitution of Nickel and Tungsten or Molybdenum with Hafnium

Element Weight Percent Cobalt at least 20 Chromium 20 Hafnium up to 60

When considering a simpler mixture, the alloy may be considered withouteither Mo or W, i.e., consisting of Hf—Co—Cr only. In this instance, theHf may range up to about 60 weight percent to avoid the Co—Cr σintermetallic phase. At 60 weight percent Hf, calculated radiopacitywould be 6.9 barnes/cc. Co—Hf falls in the cubic CoHf phase and Cr—Hffalls in the FCC Cr₂Hf plus HCP αHf regime.

Examples 42-44 below are based on the nominal compositions of the ASTMF90 L-605 Alloy of Table 1 and the ASTM F562 MP-35N Alloy of Table 3 inwhich at least the nickel, and in some examples, some of the cobalt hasbeen replaced on an weight substitution basis with a refractory metal,molybdenum. Example 45 further replaces the tungsten of L-605 (or isrelative to MP-35N, which already includes some molybdenum) withmolybdenum so that the alloy is essentially a ternary Co—Cr—Mo alloy.Trace elements such as beryllium, boron, carbon, iron, manganese,phosphorus, silicon, sulfur, and titanium are not listed.

Example 42—ASTM F90 L-605 Alloy with Weight Substitution of Nickel withMolybdenum

Element Weight Percent Cobalt 55 Chromium 20 Tungsten 15 Molybdenum 10

Substituting Mo for Ni on a weight percentage basis increases thecalculated radiopacity from 3.6 to 4.4 barnes/cc. From a metallurgicalperspective, the Co—Cr, Co—W, and Cr—W will fall in the same regions asfor L-605. Otherwise the alloy will contain a mixture of HCP εCo and HCPκ phases, BCC Cr and BCC Mo phases, and solid solution Mo and W phases.

Example 43—ASTM F90 L-605 Alloy with Weight Substitution of Nickel and aPortion of the Cobalt with Molybdenum

Element Weight Percent Cobalt at least 20 Chromium 20 Tungsten 15Molybdenum up to 45

As with the above alloys of Ag, Au, and Hf, here it is assumed that Crand W are not changed, thus Co—Cr, Co—W, and Cr—W are the same as forL-605. From a metallurgical phase diagram perspective, Mo may beincluded up to about 45 weight percent. At 45 weight percent Mo, thisgives a radiopacity of 7.2 barnes/cc and metallurgically would result ina mix of rhombohedral ε and BCC Mo, BCC Cr and BCC Mo, and BCC Mo andBCC W phases.

Example 44—ASTM F562 MP-35N Alloy with Weight Substitution of Nickelwith Molybdenum

Element Weight Percent Cobalt 35 Chromium 20 Molybdenum 45

Utilizing a straight substitution of molybdenum for nickel on a weightpercentage basis increases the radiopacity from 3.4 barnes/cc to 5.8barnes/cc. From a metallurgical perspective, Co—Cr falls in the sameregion as MP-35N. Co—Mo and Cr—Mo shift, as the Mo has increased by 35weight percentage points. Co—Mo shifts into the rhombohedral ε phaseregion, and Cr—Mo stays in the BCC Cr and BCC Mo regime, shifting closerto the Mo side of the phase diagram.

Example 45—ASTM F90 L-605 Alloy or ASTM F562 MP-35N Alloy with WeightSubstitution of Nickel and Tungsten or a Portion of the Cobalt withMolybdenum

Element Weight Percent Cobalt at least 20 Chromium 20 Molybdenum up to60

When considering a simpler mixture, the alloy may be considered witheven more Mo, without W (in the case of L-605), i.e., consisting ofMo—Co—Cr only. In the case of a modified MP-35N alloy, some of thecobalt may be replaced to further increase Mo content. Avoiding theCo—Cr σ intermetallic phase, Mo may be used up to 60 weight percent.This increases the radiopacity to 7.0 barnes/cc. This would shift theCo—Mo interaction into the rhombohedral ε and BCC Mo phase regime. TheCr—Co would remain in the BCC Cr and BCC Mo regime, shifting furthertoward the Mo side of the phase diagram.

Examples 46-49 below are based on the nominal compositions of the ASTMF90 L-605 Alloy of Table 1 and the ASTM F562 MP-35N Alloy of Table 3 inwhich at least the nickel, and in some examples, some of the cobalt hasbeen replaced on an weight substitution basis with a refractory metal,niobium. Example 50 further replaces the tungsten of L-605 or themolybdenum of MP-35N with niobium so that the alloy is essentially aternary Co—Cr—Nb alloy. Trace elements such as beryllium, boron, carbon,iron, manganese, phosphorus, silicon, sulfur, and titanium are notlisted.

Example 46—ASTM F90 L-605 Alloy with Weight Substitution of Nickel withNiobium

Element Weight Percent Cobalt 55 Chromium 20 Tungsten 15 Niobium 10

Substituting Nb for Ni on a weight percentage basis increases thecalculated radiopacity from 3.6 to 4.2 barnes/cc. From a metallurgicalperspective, the Co—Cr, Co—W, and Cr—W will fall in the same regions asfor L-605. Otherwise the alloy will contain a mixture of HCP εCo and HCPNbCo₃ phases, BCC Cr and BCC Cr₂Nb phases, and solid solution Nb and Wphases.

Example 47—ASTM F90 L-605 Alloy with Weight Substitution of Nickel and aPortion of the Cobalt with Niobium

Element Weight Percent Cobalt at least 20 Chromium 20 Tungsten 15Niobium up to 45

As with the above alloys of Ag, Au, Hf, and Mo, here it is assumed thatCr and W are not changed, thus Co—Cr, Co—W, and Cr—W are the same as forL-605. From a metallurgical phase diagram perspective, Nb may beincluded up to about 45 weight percent. At 45 weight percent Nb, thisgives a radiopacity of 6.3 barnes/cc and metallurgically would result ina mix of rhombohedral Nb₆Co₇ and BCC Nb, FCC Cr₂Nb and BCC Nb, and BCCNb and BCC W phases.

Example 48—ASTM F562 MP-35N Alloy with Weight Substitution of Nickelwith Niobium

Element Weight Percent Cobalt 35 Chromium 20 Molybdenum 10 Niobium 35

Utilizing a straight substitution of niobium for nickel on a weightpercentage basis increases the radiopacity from 3.4 barnes/cc to 5.3barnes/cc. From a metallurgical perspective, Co—Cr, Co—Mo, and Cr—Mofall in the same regions as MP-35N. Other phases will includerhombohedral Nb₆Co₇ and BCC Nb phases, FCC Cr₂Nb and BCC Nb phases, andBCC Nb and BCC Mo phases.

Example 49—ASTM F562 MP-35N Alloy with Weight Substitution of Nickel anda Portion of the Cobalt with Niobium

Element Weight Percent Cobalt at least 20 Chromium 20 Molybdenum 10Niobium up to 50

While avoiding the Co—Cr σ intermetallic phase Nb may be included up to50 weight percent. This increases radiopacity to 6.1 barnes/cc.Metallurgically, this results in the presence of rhombohedral Nb₆Co₇ andBCC Nb phases, FCC Cr₂Nb and BCC Nb phases, and BCC Nb and BCC Mophases.

Example 50—ASTM F90 L-605 Alloy or ASTM F562 MP-35N Alloy with WeightSubstitution of Nickel and Tungsten or Molybdenum with Niobium

Element Weight Percent Cobalt at least 20 Chromium 20 Niobium up to 60

When considering a simpler mixture, the alloy may be considered withouteither Mo or W, i.e., consisting of Nb—Co—Cr only. In this instance, theNb may range up to about 60 weight percent to avoid the Co—Cr σintermetallic phase. At 60 weight percent Nb, calculated radiopacitywould be 5.9 barnes/cc. Co—Nb falls in the rhombohedral Nb₆Co₇ and BCCNb regime, while the Cr—Nb falls in the FCC Cr₂Nb and BCC Nb regime.

Examples 51-54 below are based on the nominal compositions of the ASTMF90 L-605 Alloy of Table 1 and the ASTM F562 MP-35N Alloy of Table 3 inwhich at least the nickel, and in some examples, some of the cobalt hasbeen replaced on an weight substitution basis with a refractory metal,rhenium. Example 55 further replaces the tungsten of L-605 or themolybdenum of MP-35N with rhenium so that the alloy is essentially aternary Co—Cr—Re alloy. Trace elements such as beryllium, boron, carbon,iron, manganese, phosphorus, silicon, sulfur, and titanium are notlisted.

Example 51—ASTM F90 L-605 Alloy with Weight Substitution of Nickel withRhenium

Element Weight Percent Cobalt 55 Chromium 20 Tungsten 15 Rhenium 10

Substituting Re for Ni on a weight percentage basis increases thecalculated radiopacity from 3.6 to 4.4 barnes/cc. From a metallurgicalperspective, the Co—Cr, Co—W, and Cr—W will fall in the same regions asfor L-605. Otherwise the alloy will contain a mixture of HCP εCo and HCPRe phases, BCC Cr and BCC Re phases, and the Re—W will containtetragonal σ phase and BCC W phase.

Example 52—ASTM F90 L-605 Alloy with Weight Substitution of Nickel and aPortion of the Cobalt with Rhenium

Element Weight Percent Cobalt at least 20 Chromium 20 Tungsten 15Rhenium up to 45

As with the above alloys of Ag, Au, Hf, Mo, and Nb, here it is assumedthat Cr and W are not changed, thus Co—Cr, Co—W, and Cr—W are the sameas for L-605. From a metallurgical phase diagram perspective, Re may beincluded up to about 45 weight percent. At 45 weight percent Re, thisgives a radiopacity of 8.0 barnes/cc and metallurgically would result ina mix of HCP (εCo,Re), BCC Cr and tetragonal σ(Cr₂Re₃), and BCC χ andHCP Re phases.

Example 53—ASTM F562 MP-35N Alloy with Weight Substitution of Nickelwith Rhenium

Element Weight Percent Cobalt 35 Chromium 20 Molybdenum 10 Rhenium 35

Utilizing a straight substitution of rhenium for nickel on a weightpercentage basis increases the radiopacity from 3.4 barnes/cc to 6.1barnes/cc. From a metallurgical perspective, Co—Cr, Co—Mo, and Cr—Mofall in the same regions as MP-35N. Other phases will include HCP(εCo,Re), BCC Cr and BCC Re phases, and BCC Mo and BCC χ phases.

Example 54—ASTM F562 MP-35N Alloy with Weight Substitution of Nickel anda Portion of the Cobalt with Rhenium

Element Weight Percent Cobalt at least 20 Chromium 20 Molybdenum 10Rhenium up to 50

While avoiding the Co—Cr σ intermetallic phase Re may be included up to50 weight percent. This increases radiopacity to 7.8 barnes/cc.Metallurgically, this results in the presence of HCP (εCo,Re), BCC Crand tetragonal σ(Cr₂Re₃), and BCC Mo and BCC χ phases.

Example 55—ASTM F90 L-605 Alloy or ASTM F562 MP-35N Alloy with WeightSubstitution of Nickel and Tungsten or Molybdenum with Rhenium

Element Weight Percent Cobalt at least 20 Chromium 20 Rhenium up to 60

When considering a simpler mixture, the alloy may be considered withouteither Mo or W, i.e., consisting of Re—Co—Cr only. In this instance, theRe may range up to about 60 weight percent to avoid the Co—Cr σintermetallic phase. At 60 weight percent Re, calculated radiopacitywould be 8.1 barnes/cc. Co—Re falls in the HCP (εCo,Re) regime whileCr—Re falls into the BCC Cr and tetragonal σ(Cr₂Re₃) regime.

Examples 56-59 below are based on the nominal compositions of the ASTMF90 L-605 Alloy of Table 1 and the ASTM F562 MP-35N Alloy of Table 3 inwhich at least the nickel, and in some examples, some of the cobalt hasbeen replaced on an weight substitution basis with a refractory metal,tantalum. Example 60 further replaces the tungsten of L-605 or themolybdenum of MP-35N with tantalum so that the alloy is essentially aternary Co—Cr—Ta alloy. Trace elements such as beryllium, boron, carbon,iron, manganese, phosphorus, silicon, sulfur, and titanium are notlisted.

Example 56—ASTM F90 L-605 Alloy with Weight Substitution of Nickel withTantalum

Element Weight Percent Cobalt 55 Chromium 20 Tungsten 15 Tantalum 10

Substituting Ta for Ni on a weight percentage basis increases thecalculated radiopacity from 3.6 to 4.4 barnes/cc. From a metallurgicalperspective, the Co—Cr, Co—W, and Cr—W will fall in the same regions asfor L-605. Otherwise the alloy will contain a mixture of HCP εCo andCo₇Ta₂, BCC Cr and FCC Cr₂Ta, and BCC (Ta,W) phases.

Example 57—ASTM F90 L-605 Alloy with Weight Substitution of Nickel and aPortion of the Cobalt with Tantalum

Element Weight Percent Cobalt at least 20 Chromium 20 Tungsten 15Tantalum up to 45

As with the above alloys of Ag, Au, Hf, Mo, Nb and Re, here it isassumed that Cr and W are not changed, thus Co—Cr, Co—W, and Cr—W arethe same as for L-605. From a metallurgical phase diagram perspective,Ta may be included up to about 45 weight percent. At 45 weight percentTa, this gives a radiopacity of 7.9 barnes/cc and metallurgically wouldresult in a mix of FCC λ₂ (Co₂Ta) and rhombohedral Co₆Ta₇, FCC Cr₂Ta andBCC Ta, and BCC (Ta,W) phases.

Example 58—ASTM F562 MP-35N Alloy with Weight Substitution of Nickelwith Tantalum

Element Weight Percent Cobalt 35 Chromium 20 Molybdenum 10 Tantalum 35

Utilizing a straight substitution of tantalum for nickel on a weightpercentage basis increases the radiopacity from 3.4 barnes/cc to 6.1barnes/cc. From a metallurgical perspective, Co—Cr, Co—Mo, and Cr—Mofall in the same regions as MP-35N. Other phases will include Co₇Ta₂ andHCP λ₃, FCC Cr₂Ta, and BCC Mo and BCC Ta phases.

Example 59—ASTM F562 MP-35N Alloy with Weight Substitution of Nickel anda Portion of the Cobalt with Tantalum

Element Weight Percent Cobalt at least 20 Chromium 20 Molybdenum 10Tantalum up to 50

While avoiding the Co—Cr σ intermetallic phase Ta may be included up to50 weight percent. This increases radiopacity to 7.7 barnes/cc.Metallurgically, this results in the presence of Co₆Ta₇, FCC Cr₂Ta andBCC Ta, and BCC Mo and BCC Ta phases.

Example 60—ASTM F90 L-605 Alloy or ASTM F562 MP-35N Alloy with WeightSubstitution of Nickel and Tungsten or Molybdenum with Tantalum

Element Weight Percent Cobalt at least 20 Chromium 20 Tantalum up to 60

When considering a simpler mixture, the alloy may be considered withouteither Mo or W, i.e., consisting of Ta—Co—Cr only. In this instance, theTa may range up to about 60 weight percent to avoid the Co—Cr σintermetallic phase. At 60 weight percent Ta, calculated radiopacitywould be 7.9 barnes/cc. Co—Ta falls in the rhombohedral Co₆Ta₇ regimeand Cr—Ta falls in the FCC Cr₂Ta and BCC Ta regime.

Examples 61-64 below are based on the nominal compositions of the ASTMF90 L-605 Alloy of Table 1 and the ASTM F562 MP-35N Alloy of Table 3 inwhich at least the nickel, and in some examples, some of the cobalt hasbeen replaced on an weight substitution basis with a refractory metal,tungsten. The modified L-605 alloys are essentially ternary Co—Cr—Walloys. Trace elements such as beryllium, boron, carbon, iron,manganese, phosphorus, silicon, sulfur, and titanium are not listed.

Example 61—ASTM F90 L-605 Alloy with Weight Substitution of Nickel withTungsten

Element Weight Percent Cobalt 55 Chromium 20 Tungsten 25

Substituting W for Ni on a weight percentage basis increases thecalculated radiopacity from 3.6 to 4.4 barnes/cc. From a metallurgicalperspective, Co—Cr will fall in the same region as for L-605. Otherwise,the alloy will contain a mixture of HCP εCo and HCP Co₃W, and BCC(α₁+α₂) phases. Examples 133-136 below describe other examples of Co—Cralloys that include nickel, and tungsten content greater than 15% byweight, in which a primarily single-phase FCC microcrystalline structureis provided.

Example 62—ASTM F90 L-605 Alloy with Weight Substitution of Nickel and aPortion of the Cobalt with Tungsten

Element Weight Percent Cobalt at least 35 Chromium 20 Tungsten up to 45

It is assumed that Cr is not changed, thus Co—Cr is the same as forL-605. From a metallurgical phase diagram perspective, W may be includedup to about 45 weight percent. At 45 weight percent W, this gives aradiopacity of 7.9 barnes/cc and metallurgically would result in a mixof rhombohedral Co₇W₆ and HCP Co₃W, and BCC (α₁+α₂) phases. Examples133-136 below describe other examples of Co—Cr alloys that includenickel, and tungsten content greater than 15% by weight, in which aprimarily single-phase FCC microcrystalline structure is provided.

Example 63—ASTM F562 MP-35N Alloy with Weight Substitution of Nickelwith Tungsten

Element Weight Percent Cobalt 35 Chromium 20 Molybdenum 10 Tungsten 35

Utilizing a straight substitution of tungsten for nickel on a weightpercentage basis increases the radiopacity from 3.4 barnes/cc to 6.1barnes/cc. From a metallurgical perspective, Co—Cr, Co—Mo, and Cr—Mofall in the same regions as MP-35N. Other phases will include HCP Co₃W,BCC (α₁+α₂), and BCC Mo and BCC W phases. Examples 133-136 belowdescribe other examples of Co—Cr alloys that include nickel, may be voidof molybdenum, and include tungsten content greater than 15% by weight,in which a primarily single-phase FCC microcrystalline structure isprovided.

Example 64—ASTM F562 MP-35N Alloy with Weight Substitution of Nickel anda Portion of the Cobalt with Tungsten

Element Weight Percent Cobalt at least 20 Chromium 20 Molybdenum 10Tungsten up to 50

While avoiding the Co—Cr σ intermetallic phase W may be included up to50 weight percent. This increases radiopacity to 7.7 barnes/cc.Metallurgically, this results in the presence of rhombohedral Co₇W₆ BCC(α₁+α₂) and BCC Mo and BCC W phases. Another example may furtherincrease the tungsten to up to 60% by replacing the molybdenum withtungsten. This would further increase radiopacity, and result in thesame phases present as described relative to an alloy including up to 50weight percent tungsten. Of course, such a modified alloy could also berelative to (or derived from) L-605, as both would include at least 20%Co, 20% Cr, and up to 60% W. Examples 133-136 below describe otherexamples of Co—Cr alloys that include nickel, may be void of molybdenum,and which include tungsten content greater than 15% by weight, in whicha primarily single-phase FCC microcrystalline structure is provided.

Examples 65-68 below are based on the nominal compositions of the ASTMF90 L-605 Alloy of Table 1 and the ASTM F562 MP-35N Alloy of Table 3 inwhich at least the nickel, and in some examples, some of the cobalt hasbeen replaced on an weight substitution basis with a refractory metal,zirconium. Example 69 further replaces the tungsten of L-605 or themolybdenum of MP-35N with zirconium so that the alloy is essentially aternary Co—Cr—Zr alloy. Trace elements such as beryllium, boron, carbon,iron, manganese, phosphorus, silicon, sulfur, and titanium are notlisted.

Example 65—ASTM F90 L-605 Alloy with Weight Substitution of Nickel withZirconium

Element Weight Percent Cobalt 55 Chromium 20 Tungsten 15 Zirconium 10

Substituting Zr for Ni on a weight percentage basis increases thecalculated radiopacity from 3.6 to 4.1 barnes/cc. From a metallurgicalperspective, the Co—Cr, Co—W, and Cr—W will fall in the same regions asfor L-605. Otherwise the alloy will contain a mixture of HCP εCo andγ(CoZr), FCC αZrCr₂ and BCC Cr, FCC W₂Zr, and HCP (αZr) phases.

Example 66—ASTM F90 L-605 Alloy with Weight Substitution of Nickel and aPortion of the Cobalt with Zirconium

Element Weight Percent Cobalt at least 20 Chromium 20 Tungsten 15Zirconium up to 45

As with the above alloys of Ag, Au, Hf, Mo, Nb, Re, and Ta, here it isassumed that Cr and W are not changed, thus Co—Cr, Co—W, and Cr—W arethe same as for L-605. From a metallurgical phase diagram perspective,Zr may be included up to about 45 weight percent. At 45 weight percentZr, this gives a radiopacity of 5.5 barnes/cc and metallurgically wouldresult in a mix of cubic ζ(CoZr) and BCT η(CoZr), FCC αZrCr₂ and HCPαZr, and FCC W₂Zr and HCP αZr phases.

Example 67—ASTM F562 MP-35N Alloy with Weight Substitution of Nickelwith Zirconium

Element Weight Percent Cobalt 35 Chromium 20 Molybdenum 10 Zirconium 35

Utilizing a straight substitution of zirconium for nickel on a weightpercentage basis increases the radiopacity from 3.4 barnes/cc to 4.8barnes/cc. From a metallurgical perspective, Co—Cr, Co—Mo, and Cr—Mofall in the same regions as MP-35N. Other phases will include FCCε(CoZr) and cubic ζ(CoZr), FCC αZrCr₂ and HCP αZr, and FCC Mo₂Zr, andBCC Mo phases.

Example 68—ASTM F562 MP-35N Alloy with Weight Substitution of Nickel anda Portion of the Cobalt with Zirconium

Element Weight Percent Cobalt at least 20 Chromium 20 Molybdenum 10Zirconium up to 50

While avoiding the Co—Cr σ intermetallic phase Zr may be included up to50 weight percent. This increases radiopacity to 5.3 barnes/cc.Metallurgically, this results in the presence of cubic ζ(CoZr) and BCTη(CoZr), FCC αZrCr₂ and HCP αZr, FCC Mo₂Zr, and HCP αZr phases.

Example 69—ASTM F90 L-605 Alloy or ASTM F562 MP-35N Alloy with WeightSubstitution of Nickel and Tungsten or Molybdenum with Zirconium

Element Weight Percent Cobalt at least 20 Chromium 20 Zirconium up to 60

When considering a simpler mixture, the alloy may be considered withouteither Mo or W, i.e., consisting of Zr—Co—Cr only. In this instance, theZr may range up to about 60 weight percent to avoid the Co—Cr σintermetallic phase. At 60 weight percent Zr, calculated radiopacitywould be 5.0 barnes/cc. Co—Zr falls close to the BCT η(CoZr) phase, butwould also likely include some cubic ζ(CoZr) phase as well. The Cr—Zrfalls in the FCC αZrCr₂ and HCP αZr phase regime.

Exemplary alloys of Examples 25-69, even those with relatively complexphase diagrams, are expected to provide viable alloys for use in stentfabrication. Enhancing the radiopacity of the alloy while remainingviable from metallurgical and engineering perspectives allows thefabrication of improved medical devices, particularly stents wheregreater radiopacity is beneficial.

Examples 70-73 describe particular ternary cobalt-chromium-iridiumalloys that are somewhat similar to Examples 7-8, but which areessentially ternary alloys and do not include elements other thancobalt, chromium, and iridium. Such an embodiment may include chromiumat a level from about 10 to about 25 atomic percent, more particularlyfrom about 15 to about 25 (e.g., about 20 atomic percent) atomic percentto impart the desired tightly adhering Cr₂O₃ oxide layer that providesexcellent corrosion resistance. The cobalt and iridium levels may bevaried in virtually any ratio, depending on desired radiopacity, degreeof ferromagnetism, and mechanical strength because cobalt and iridiumare mutually soluble in one another and therefore do not formundesirable intermetallic phases. In order to avoid ferromagnetism atroom temperature, the ratio of iridium to cobalt may be selected so asto be greater than about 1:1 on an atomic percentage basis. The resultis a radiopaque, corrosion resistant, and relatively inexpensive ternaryalloy system for stents. Iridium is attractive because it has slightlybetter radiopacity than platinum and has a cost approximately half thatof platinum and similar to that of palladium. Similar ternary alloysincluding only cobalt, chromium, and a metal other than iridium (e.g.,Pt, Pd, Ru, Rh, or Os) could similarly be provided. Such ternary alloysmay include similar atomic fractions as those described above and inExamples 70-73 but in which the Iridium is substituted with Pt, Pd, Ru,Rh, or Os. Similar ternary alloys could also be formed from Co, Cr, anda refractory metal or precious metal (i.e., silver or gold).

According to one embodiment, such a ternary alloy is not based on anyexisting commercially available alloy composition such as L-605 orMP-35N so that it does not contain extra elements such as tungsten,molybdenum, iron, manganese, etc. and thus minimizes the complexity interms of intermetallics, precipitate formation, etc.

Example 70—Ternary Cobalt-Chromium-Iridium Alloy

Element Atomic Percent Cobalt 35 Chromium 20 Iridium 45

Example 71—Ternary Cobalt-Chromium-Iridium Alloy

Element Atomic Percent Cobalt 30 Chromium 20 Iridium 50

Example 72—Ternary Cobalt-Chromium-Iridium Alloy

Element Atomic Percent Cobalt 25 Chromium 20 Iridium 55

Example 73—Ternary Cobalt-Chromium-Iridium Alloy

Element Atomic Percent Cobalt 20 Chromium 20 Iridium 60

As mentioned previously, a platinum group metal, refractory metal, orprecious metal may replace elements in addition to the nickel of anexisting commercially available alloy such as L-605, MP-35N, Elgiloy, orPhynox. For example, in L-605, the nickel is included as an austeniticstabilizer. Nickel and the platinum group elements palladium andplatinum are group 10 elements. Thus, platinum and palladium may also beexpected to act as austenitic stabilizers in cobalt. In addition, cobaltand each of the three group 10 elements (nickel, palladium, andplatinum) are mutually dissolvable in each other. Platinum and/orpalladium may be substituted for nickel in L-605 to improve radiopacity.Where insufficient radiopacity is provided under atomic percentagesubstitution as described in Examples 1 and 3, at least some of thecobalt of an alloy such as L-605 may also be replaced with the platinumgroup metal to further increase the radiopacity. Examples 74-75 andExamples 76-77 describe such examples that are similar to 1 and 3,respectively, but also replace at least a portion of the cobalt tofurther increase radiopacity. Similar examples could be provided basedon alloys other than L-605 (e.g., MP-35N, Elgiloy, or Phynox)

Example 74—ASTM F90 L-605 Alloy with Atomic Substitution of Nickel and aPortion of the Cobalt with Platinum

Element Atomic Percent Cobalt 48.9 Chromium 24.4 Tungsten 5.2 Platinum15.8 Manganese (maximum) 2.3 Iron (maximum) 3.4

Example 75—ASTM F90 L-605 Alloy with Atomic Substitution of Nickel and aPortion of the Cobalt with Platinum

Element Atomic Percent Cobalt 43.9 Chromium 24.4 Tungsten 5.2 Platinum20.8 Manganese (maximum) 2.3 Iron (maximum) 3.4

Example 76—ASTM F90 L-605 Alloy with Atomic Substitution of Nickel and aPortion of the Cobalt with Palladium

Element Atomic Percent Cobalt 48.9 Chromium 24.4 Tungsten 5.2 Palladium15.8 Manganese (maximum) 2.3 Iron (maximum) 3.4

Example 77—ASTM F90 L-605 Alloy with Atomic Substitution of Nickel and aPortion of the Cobalt with Palladium

Element Atomic Percent Cobalt 43.9 Chromium 24.4 Tungsten 5.2 Palladium20.8 Manganese (maximum) 2.3 Iron (maximum) 3.4

As mentioned previously, a platinum group metal, refractory metal, orprecious metal may replace elements in addition to the nickel of anexisting commercially available alloy such as L-605, MP-35N, Elgiloy, orPhynox. Several of the above embodiments include substitution of aportion of the cobalt in addition to substitution of the nickel. Anotherembodiment may specifically substitute the refractory metal (e.g.,molybdenum or tungsten) present within the commercial alloy, replacingthis refractory metal with a platinum group metal (particularlypreferred substituting platinum group metals include Pt, Pd, Ir, and Rh.Another embodiment may substitute with another refractory metal (e.g.,substitute Mo with Re). Another embodiment may substitute the refractorymetal with iron, which if done, is may be present in a small amount, asdescribed herein. Many of these alloy embodiments may also replace thenickel, and optionally a portion of the cobalt, chromium, or even both,with a platinum group metal, particularly preferred of which would bePt.

For example, a base research alloy which still includes the refractorymetal (e.g., molybdenum) is herein designated MP1, and has a compositionas shown below in Table 5. MP1 may be considered to be a more heavilysubstituted variant of MP-35N, as the amount of chromium is lower (13.5%vs. 20% by weight) and the amount of molybdenum is lower (6.7% vs. 10%).Some of the chromium and molybdenum, as well as all the nickel and aportion of the cobalt has been replaced with platinum.

TABLE 5 MP1 Alloy Element Weight Percent Atomic Percent Cobalt 23.3 39.0Chromium 13.5 25.6 Molybdenum 6.7 6.9 Platinum 56.5 28.5

In evaluating various of the earlier described cobalt-chromium-platinumgroup alloys described above in conjunction with Examples 1-24, it wasfound that as ingots were prepared by melting and then worked toevaluate their workability, a greater understanding of ambienttemperature workability (i.e., cold workability) of these alloys wasgained. Ordinarily significant reduction in workability when platinum isadded to 316L stainless steel at greater than 33 weight percent isexpected. However, this reduction in workability did not occur in atleast some of the present alloy systems described herein. Rather, someof the initial platinum substituted alloy melts with greater than 33weight percent platinum were workable as evidenced by being rolled at upto 50% deformation.

One of the most promising precious metal substitution alloys melted andprocessed was MP1, described in Table 5 above. Other alloys with greaterpercentages of Pd that were investigated with off stoichiometric alloycompositions showed good workability, but resulted in lower than desireddensities. Pd (density of 12.02 g/cm³) is significantly less dense thanPt (density of 21.45 g/cm³). Thus, substitution with platinum may beparticularly preferred. Alloy MP1 maintains a high density (12.8 g/cm³)and a relative radiopacity of 9.8 barnes/cm³. While this alloy showedgood workability after casting, microstructural changes resulted insomewhat lower workability after heat treatment.

In order to further improve the workability of the MP1 alloy, additionalquaternary (and in some cases pentenary) alloys were investigated byreplacing the molybdenum in the MP1 alloy, as described above. Example87 is a ternary alloy in which the molybdenum is replaced withadditional cobalt. Examples 78-89 in Table 6 below show the resultingcompositions. Refractory metal elements such as molybdenum and tungstenare typically used for strengthening, but can also reduce workability.The specific substitutions shown in Examples 78-89 of Table 6 are basedon phase diagram analysis. Examples 81, 85, and 87 were actually formedby melting, and then worked to evaluate their workabilitycharacteristics. Of these three, Examples 85 and 87 showed the best castworkability in rolling, with Example 85 being slightly better.

TABLE 6 Variants of Mfg With Substitution of Molybdenum Pt Co Cr Fe IrPd Re Rh wt % wt % wt % wt % wt % wt % wt % wt % Density RR Alloy at %at % at % at % at % at % at % at % (g/cm³) (barnes/cm³) Ex. 78 56.5 23.313.5 6.7 13.0 10.1 (28.7) (39.2) (25.8) (6.2) Ex. 79 52 23.3 18 6.7 12.39.2 (24.9) (36.9) (32.3) (5.9) Ex. 80 54 23.3 16 6.7 12.6 9.6 (26.5)(37.9) (29.5) (6.0) Ex. 81 54.2 23.3 13.5 9.0 12.8 10.1 (27.3) (38.9)(25.5) (8.3) Ex. 82 43.7 23.3 18 10 5 12.1 9.1 (20.6) (36.4) (31.9)(8.6) (2.5) Ex. 83 56.5 23.3 13.5 6.7 13.4 10.0 (29.5) (40.3) (26.5)(3.7) Ex. 84 52.9 23.1 16 5 3 12.7 9.0 (26.2) (37.9) (29.8) (4.5) (1.6)Ex. 85 56.5 23.3 13.5 6.7 12.5 8.9 (27.2) (37.1) (24.4) (11.3) Ex. 8656.5 23.3 13.5 6.7 13.0 10.1 (28.7) (39.2) (25.7) (6.4) Ex. 87 56.5 30.013.5 12.7 9.0 (27.4) (48.1) (24.5) Ex. 88 56.5 23.3 13.5 6.7 13.5 10.2(29.6) (40.4) (26.5) (3.6) Ex. 89 40 23.3 13.5 13.2 10 12.1 10.0 (19.0)(36.6) (24.0) (11.5) (9.0)

Generally, many of Examples 78-89 are nickel-free, molybdenum-freecobalt-based alloys comprising from about 18 weight percent to about 39weight percent cobalt, from about 10 weight percent to about 25 weightpercent chromium, from about 40 weight percent to about 65 weightpercent platinum, and from about 5 weight percent to about 25 weightpercent of one or more other platinum group metals, refractory metals,or combinations thereof. In another embodiment, and as will be apparentfrom Examples 78-89, the cobalt-based alloy may comprise from about 18weight percent to about 30 weight percent cobalt, from about 10 weightpercent to about 20 weight percent chromium, and from about 45 weightpercent to about 60 weight percent platinum. In another embodiment, andas will be apparent from Examples 78-89, the cobalt-based alloy maycomprise from about 18 weight percent to about 25 weight percent cobalt,from about 10 weight percent to about 15 weight percent chromium, andfrom about 50 weight percent to about 60 weight percent platinum.Example 85 substitutes with iron rather than a platinum group metal orrefractory metal, while Example 87 substitutes the molybdenum withadditional cobalt to result in a ternary alloy. In an embodiment, thealloy may be substantially free or completely free of other refractorymetals, other than molybdenum (e.g., tungsten).

Examples 78-81, 83, and 86-87 are quaternary alloys comprising cobalt,chromium, platinum, and one other platinum group metal or refractorymetal. Examples 82, 84, and 89 are pentenary alloy comprising cobalt,chromium, platinum, and one or more other platinum group metals,refractory metals, or combinations thereof (i.e., two additionalelements are selected from platinum group metals, refractory metals, orcombinations).

Example 85 can more generally be described as a molybdenum-freecobalt-based alloy comprising from about 18 weight percent to about 39weight percent cobalt, from about 10 weight percent to about 25 weightpercent chromium, from about 40 weight percent to about 65 weightpercent platinum, and from about 5 weight percent to about 10 weightpercent iron. In one embodiment, iron is present at less than 10 weightpercent by weight, or less than 8 weight percent.

With respect to an embodiment including iron, (e.g., Example 85), it isnoted that the Fe—Cr phase diagram does include an intermetallic a phasebetween about 43 and about 48 weight percent chromium (and 52-57 weightpercent iron). Although this phase is only formed at elevatedtemperatures (e.g., from about 440° C. to about 830° C.), such a phasemay possibly remain even after such an alloy is cooled to roomtemperatures. As such, in some embodiments, it may be desired tomaintain the ratio of iron to chromium outside of the intermetallic aphase. This phase occurs just below a 1:1 weight ratio of Cr:Fe. In oneembodiment, the weight fraction of chromium is greater than the weightfraction of iron so as to clearly avoid this phase. Because chromium istypically present at a significantly higher level (e.g., 10% plus, 15%plus, etc.) than the iron, this will typically not be an issue. Forexample, Example 85 includes a Cr:Fe weight ratio of about 2:1. Evenwhere the weight ratio of Cr to Fe is lower (e.g., 1:1, or even 0.8:1)such alloys may still be suitable if no intermetallic is present at theconditions of use (e.g., where the intermetallic phase does not persistat ambient temperature (e.g., near 20° C.)).

Example 87 can more generally be described as a molybdenum-freecobalt-based alloy comprising from about 18 weight percent to about 39weight percent cobalt, from about 10 weight percent to about 25 weightpercent chromium, from about 40 weight percent to about 65 weightpercent platinum. The alloy is ternary, the molybdenum of MP1 havingbeen replaced with additional cobalt.

Although the compositions shown in Table 6 are based on MP1 (which isbased on MP-35N), it will be understood that alloy variants of L-605,Elgiloy, and Phynox can also be provided by substituting for nickel, forrefractory elements (e.g., tungsten in L-605, molybdenum for Elgiloy andPhynox), as well as substituting for some cobalt, some chromium, andiron or other low fraction elements. When these alloys are reduced toquaternary or pentenary form with relative radiopacities greater than5.5 barnes/cm³, the possible elemental compositions may be similar tothose shown above in Table 6, as well as various examples discussedpreviously. As such, these variants of L-605, Elgiloy, and Phynox arealso within the scope of the present disclosure.

TABLE 7 ASTM F90 L-605 Alloy Element Weight Percent Atomic PercentVolume Percent Cobalt 53.4 57.4 55.0 Chromium 20 24.4 25.4 Tungsten 155.2 7.1 Nickel 10 10.8 10.3 Manganese 1.5 1.7 1.9 Carbon 0.1 0.5 0.4

Table 7 again shows compositional alloy data for L-605, includingslightly differing amounts for cobalt due to a slightly different amountof manganese, as well as the inclusion of a trace amount of carbon.Iron, phosphorus, silicon, and sulfur may also be present in traceamounts not shown in Table 7, which may decrease the amount of cobalt,which may comprise the balance of the alloy.

In further evaluating various of the earlier described cobalt-chromiumalloys described above in conjunction with the previous Examples, it wasfound that additional austenitic stabilization may be needed. Asdescribed above, austenitic stabilization allows for the material to behot and cold worked during processing from ingot to stent.

Cobalt is an allotropic elemental material, and at temperatures up to422° C. has a hexagonal close-packed (ε-Co, HCP) crystalline structure,while above 422° C. it has a face-center-cubic (α-Co, FCC) crystallinestructure. The e-HCP microstructure is relatively brittle and preventsappreciable cold working in the material, while the α-FCC, or austeniticcobalt, is more ductile and allows for cold and hot working forprocessing purposes. As cobalt is alloyed with other elements, thetemperature of the ε-Co to α-Co transformation may increase or decreasebased on the microstructure, bonding valence, electronegativity, andatom size of the alloying element(s). The response of each element withcobalt is shown in their associated binary phase diagrams. If thetransformation temperature decreases with the addition of the alloyingelement there is an enlarged a field and these elements are consideredFCC stabilizers. FCC stabilizers include, but may not be limited to, Al,B, Cu, Ti, Zr, C, Sn, Nb, Mn, Fe, and Ni.

If the transformation temperature increases with the addition of thealloying element, then there is a restricted a field and these elementsare considered HCP stabilizers. HCP stabilizers include, but may not belimited to, Si, Ge, Ar, Sb, Cr, Mo, W, Ta, Re, Ru, Os, Rh, Ir, and Pt.In some Co binary alloys, the transition temperature increases forε-Co→α-Co, while the transformation temperature for α-Co→ε-Co decreases,which makes the transformation more sluggish, and these elements areconsidered to have a combined stabilization effect (i.e., they maystabilize both FCC and HCP phases), with the phase present at any givencondition being stabilized to retard change to the other phase. Elementswith a combined effect on the transformation temperature in cobaltinclude: Be, Pb, V, Pd, Ga, Au.

In the L-605 alloy (composition shown in Tables 1 and 7), nickel servesas an austenitic stabilizer of cobalt, which allows the alloy to beprocessed using both hot and cold working methods. As described herein,in an embodiment it is desirable for the nickel to be removed tominimize any potential allergy concerns. However, the other two mainconstituents (Cr and W) in L-605 may not facilitate FCC stabilization ofthe cobalt, and may instead increase the propensity for HCP structuresto form upon working the material.

Furthermore, as described above, there is a desire to increase theradiopacity of the stent material with addition of platinum groupmetals, refractory metals, and/or precious metals, such as silver (Ag),gold (Au), hafnium (Hf), iridium (Ir), molybdenum (Mo), palladium (Pd),platinum (Pt), rhenium (Re), rhodium (Rh), tantalum (Ta), tungsten (W),and/or zirconium (Zr), which are more radiopaque than nickel. Radiopaqueelements such as Au, Ir, Pd, Pt, Re, Ta, and W all significantly improveradiopacity of the material as their relative radiopacity is at leastfour times higher than nickel; however, none of these elements may be,strictly speaking, FCC stabilizers. Therefore, an increase inconcentration of one or more FCC austenitic stabilizers may therefore beimportant for the workability of an alloy material based on L-605 aimedat increasing the radiopacity and limiting nickel content. Otherexamples (e.g., Examples 133-136) employ a different strategy, by whichnickel (and optionally manganese) content is maintained, as thesestabilize the FCC microstructure, but in which tungsten may be addedabove its normal solubility limit, and the alloy may be processed in away that ensures that a primarily single-phase FCC microcrystallinestructure is present, even at the super-saturated tungsten content.

The following additional examples through example 132 are based onmodification of a base L-605 alloy. It will be apparent that additionalanalogous examples may be provided based on MP-35N, Elgiloy, or Phynoxemploying the substitution techniques described herein. In addition,while the following examples employ platinum and/or palladium, it willbe understood that other platinum group metals, refractory metals,and/or precious metals may be included instead of or in addition to Ptand/or Pd to increase the radiopacity to a desired level.

Manganese (Mn) and iron (Fe) are both FCC stabilizers of cobalt basedalloys and are present in L-605 alloy in low amounts, as shown in Tables1 & 7. Since Mn is already present in the L-605 alloy, increasing thelevels of this element is not expected to adversely react with thecurrent chemistry. Increased amounts of Fe have the potential toincrease the magnetic response of the material, which may not bedesirable in an implantable medical device, although relatively lowlevels of iron as described herein may be suitable for use. Any of theabove described platinum group elements, refractory metal elements,and/or precious metals (e.g., particularly Au, Pd, Pt, Ta, and/or W)could partially or completely replace the Ni content of L-605 to provideincreased radiopacity. As platinum and palladium are in the sameperiodic table group as nickel they may be particularly good choices toreplace the nickel in L-605 to increase radiopacity. At the same time,the concentration of Mn and/or Fe may be increased to provide sufficientaustenitic FCC stabilization. Target ranges of Mn and/or Fe aredependent upon the desired level of relative radiopacity and governed bysolidification dynamics between the elements; however, a broad class ofPt or Pd L-605 modified alloys are shown below in Table 8.

TABLE 8 Mn and or Fe FCC Stabilized Co-Cr Alloys Element Atomic PercentCobalt 57.4 (39.1-57.4) Chromium 24.4 (20.1-26.0) Tungsten 5.2(4.9-5.2)  Nickel   0 to 10.8 Platinum 1.0 to 10.8 Palladium 2.0 to 20.0Manganese 1.7 to 20.0 Iron   0 to 10.8 Carbon 0.1 to 0.5 

In addition to Mn and Fe as austenitic stabilizers, maintaining some Nias a stabilizer is also an option explored in some of the examplesbelow. Also, as described above, it is desirable that relatively brittleintermetallics that may form between two or more of the components beavoided.

In an embodiment, the manganese may be present from 1 percent to about25 percent by weight, from about 1 percent to about 17 percent byweight, or from about 1 percent to about 10 percent by weight.

In another embodiment the combined weight percentages of the manganeseand any nickel (i.e., Mn+Ni) may be present from 1 percent to about 25percent by weight, from about 1 percent to about 17 percent by weight,or from about 1 percent to about 10 percent by weight.

In another embodiment the combined weight percentages of the manganese,iron, and any nickel (i.e., Mn+Fe+Ni) may be present from 1 percent toabout 25 percent by weight, from about 1 percent to about 17 percent byweight, or from about 1 percent to about 10 percent by weight.

TABLE 9A Specific Mn, Fe, and/or Ni FCC Stabilized Co-Cr AlloysComposition (at %) Alloy Co Cr Mn Ni Pd Pt Fe W C RR Example 1 57.4 24.41.7 — — 10.8 — 5.2 0.5 7.50 Example 3 57.4 24.4 1.7 — 10.8 — — 5.2 0.54.96 Example 90 49.1 24.4 10.8 — 10 — — 5.2 0.5 4.79 Example 91 49.124.4 10.8 — — 10 — 5.2 0.5 7.12 Example 92 47.4 24.4 1.7 — 10 — 10.8 5.20.5 4.82 Example 93 54.8 25.9 8.1 — 3.6 2 — 5.1 0.5 4.78 Example 94 55.126 7.9 — 2.9 2.7 — 4.9 0.5 4.88 Example 95 57.4 24.4 7.9 — — 4.6 — 5.20.5 5.35 Example 96 57.4 24.4 4.9 — — 7.6 — 5.2 0.5 6.40 Example 97 57.424.4 5.5 — 7.0 — — 5.2 0.5 4.53 Example 98 57.4 24.4 3.6 — 8.9 — — 5.20.5 4.75 Example 99 56.1 20.1 2.4 — 15.4 2 3.5 — 0.5 5.37 Example 10051.9 26 2.5 — 10.9 4.6 3.6 — 0.5 5.46 Example 101 57.3 21.0 2.5 — 10.94.2 3.6 0.5 5.43 Example 102 57.4 24.4 9.0 — — 3.5 — 5.2 0.5 4.97Example 103 57.4 24.4 1.7 3.3 — 7.5 — 5.2 0.5 6.42 Example 104 57.4 24.41.7 5.3 — 5.5 — 5.2 0.5 5.75 Example 105 57.4 24.4 1.7 8.0 — 2.8 — 5.20.5 4.82 Example 106 57.4 24.4 1.7 7.3 — 3.5 — 5.2 0.5 5.07 Example 10752.6 24.4 6.5 — 10.8 — — 5.2 0.5 4.91 Example 108 39.1 24.4 20.0 — 10.8— — 5.2 0.5 4.78 Example 109 52.6 24.4 3.5 3.0 10.8 — — 5.2 0.5 4.95Example 110 39.1 24.4 6.5 4.3 20.0 — — 5.2 0.5 5.84 Example 111 42.924.4 5.0 7.0 15.0 — — 5.2 0.5 5.37 Example 112 47.3 24.4 3.5 8.3 10.8 —— 5.2 0.5 4.97 Example 113 49.5 24.4 1.3 8.3 10.8 — — 5.2 0.5 4.99

TABLE 9B Specific Mn, Fe, and/or Ni FCC Stabilized Co-Cr AlloysComposition (wt %) Alloy Co Cr Mn Ni Pd Pt Fe W C Example 1 43.3 16.21.2 — — 27.0 — 12.2 0.1 Example 3 49.3 18.5 1.4 — 16.8 — — 13.9 0.1Example 114 42.7 18.7 8.7 — 15.7 — — 14.1 0.1 Example 115 37.8 16.5 7.7— — 25.4 — 12.5 0.1 Example 116 41.1 18.7 1.4 — 15.7 8.9 14.1 0.1Example 117 48.0 20.0 6.6 — 5.7 5.8 — 13.8 0.1 Example 118 48.0 20.0 6.4— 4.6 7.5 — 13.4 0.1 Example 119 48.0 19.9 8.0 — 14.0 — — 10.0 0.1Example 120 45.0 20.0 2.0 — 17.0 13.0 3.0 — 0.1 Example 121 50.0 16.02.0 — 17.0 12.0 3.0 — 0.1 Example 122 51.0 16.0 2.0 — 25.0 — 3.0 — 0.1Example 123 49.7 18.7 7.3 — — 10.1 — 14.1 0.1 Example 124 45.9 17.2 1.32.6 — 19.9 — 13.0 0.1 Example 125 47.7 17.9 1.3 4.4 — 15.1 — 13.5 0.1Example 126 50.3 18.9 1.4 7.0 — 8.1 — 14.2 0.1 Example 127 49.6 18.6 1.46.3 — 10.0 — 14.0 0.1 Example 128 45.3 18.6 5.2 — 16.8 — — 14.0 0.1Example 129 34.0 18.7 16.2 — 16.9 — — 14.1 0.1 Example 130 31.7 17.4 4.93.5 29.3 — — 13.1 0.1 Example 131 35.9 18.0 3.9 5.8 22.7 — — 13.6 0.1Example 132 42.6 18.5 1.0 7.1 16.8 — — 13.9 0.1

Generally, many of the Examples 90-132 are similar or identical to oneanother, as Table 9A reports atomic percentages, while Table 9B reportsweight percentages. The Examples of Table 9A are cobalt-based alloyscomprising from about 39.1 atomic percent to about 57.4 atomic percentcobalt, from about 20.1 to about 26 atomic percent chromium, from about1.3 atomic percent manganese to about 20 atomic percent manganese, andfrom about 2.8 atomic percent to about 20 atomic percent platinum and/orpalladium. Examples 90-102 and 107-108 of Table 9A are nickel-free.Examples 90-98 and 102-113 of Table 9A additionally include from about4.9 to about 5.2 atomic percent tungsten. Examples 92 and 99-101substitute at least a portion of the nickel of L-605 with iron, andinclude from about 3.5 atomic percent to about 10.8 atomic percent iron.All Examples of Table 9A are nickel free, or at least include a reducednickel content as compared to L-605. Examples 103-106 and 109-113include reduced nickel content, from about 3 atomic percent to about 8.3atomic percent nickel.

The Examples of Table 9B are cobalt-based alloys comprising from about31.7 weight percent to about 51 weight percent cobalt, from about 16weight percent to about 20 weight percent chromium, from about 1 weightpercent manganese to about 16.2 weight percent manganese, and from about8.1 weight percent to about 30 weight percent platinum and/or palladium.Examples 114-123 and 128-129 of Table 9B are nickel-free. Examples114-119 and 123-132 of Table 9B additionally include from about 10 toabout 14.2 weight percent tungsten. Examples 116 and 120-122 substituteat least a portion of the nickel of L-605 with iron, and include fromabout 3 weight percent to about 8.9 weight percent iron. All Examples ofTable 9B are nickel free, or at least include a reduced nickel contentas compared to L-605. Examples 124-127 and 130-132 include reducednickel content, from about 2.6 weight percent to about 7.1 weightpercent nickel. Some nickel-containing examples that include a nickelcontent that is reduced as compared to that of L-605 (10 weight percent)may contain less than 5 percent by weight nickel, or less than 3.5weight percent nickel. The manganese and/or iron content may beincreased to provide a Mn+Fe+Ni content that is as described above(e.g., 1 to 25 weight percent, 1 to 17 weight percent, or 1 to 10 weightpercent). Some flexibility may be taken with respect to the Examples.For example, similar examples may be formed that would include theamounts indicated, plus or minus 10%, plus or minus 5%, or plus or minus3% from the stated atomic percentages, weight percentages, or volumepercentages.

Table 10 below shows calculated combined Mn+Fe+Ni weight percentages forthe Examples of Table 9B.

TABLE 10 Mn + Fe + Ni Alloy Wt % Example 1 1.2 Example 3 1.4 Example 1148.7 Example 115 7.7 Example 116 10.3 Example 117 6.6 Example 118 6.4Example 119 8.0 Example 120 5.0 Example 121 5.0 Example 122 5.0 Example123 7.3 Example 124 3.9 Example 125 5.7 Example 126 8.4 Example 127 7.7Example 128 5.2 Example 129 16.2 Example 130 8.4 Example 131 9.7 Example132 8.1

In an embodiment, the combined weight percentage of the manganese, anyiron, and any nickel is from 1 to 17 weight percent, from 1 to 10 weightpercent, at least 3 weight percent, at least 4 weight percent, or atleast 5 weight percent (e.g., from 3 to 10 weight percent, 4 to 10weight percent, or 5 to 10 weight percent). The same ranges may apply toMn+Ni or Mn+Fe. The nickel content may be limited to below that of L-605alloy (10 weight percent). For example, added nickel may be present atno more than 7.1 weight percent, 7 weight percent, 6.3 weight percent,5.8 weight percent, 5 weight percent, 4.4 weight percent, 3.5 weightpercent, or 2.6 weight percent.

For example, Example 126 includes 7 weight percent nickel and 1.4 weightpercent manganese, no more than trace iron, with a combined Mn+Nicontent of 8.1 weight percent. Example 127 includes 6.3 weight percentnickel and 1.4 weight percent manganese, no more than trace iron, with acombined Mn+Ni content of 7.7 weight percent. Example 131 includes 5.8weight percent nickel and 3.9 weight percent manganese, no more thantrace iron, with a combined Mn+Ni content of 9.7 weight percent. Example132 includes 7.1 weight percent nickel and 1.0 weight percent manganese,no more than trace iron, with a combined Mn+Ni content of 8.1 weightpercent. As such, examples including 5 weight percent or more nickel(e.g., 5 to 8 weight percent or 5.8 to 7.1 weight percent) may includeMn+Ni content of 7 to 10 weight percent (e.g., 7.7 to 9.7 weightpercent). Within such examples including 5 weight percent or morenickel, manganese may be included in amounts of 1 to 10 or 1 to 5 weightpercent.

Relative radiopacities of the Examples are shown in Table 9A. Of course,those examples which are identical (but reported in weight percent inTable 9B) would have identical relative radiopacity values. Relativeradiopacity values for Examples 90-132 range from about 4.53 barnes/cm³to 7.5 barnes/cm³. In an embodiment, the relative radiopacity may begreater than 4.5 barnes/cm³ or greater than 4.6 barnes/cm³ (e.g., 4.5barnes/cm³ to 7.5 barnes/cm³, from 4.5 barnes/cm³ to 6.5 barnes/cm³ from4.6 barnes/cm³ to 7.5 barnes/cm³, or from 4.6 barnes/cm³ to 6.5barnes/cm³). In an embodiment, such relative radiopacity may be optimumfor stent strut thickness of about 60 to about 85 microns (e.g., 62microns, 81 microns).

In an embodiment, nickel and tungsten are absent. For example, Examples120, 121, and 122 describe examples based on L-605 in which thesecomponents are substituted with platinum and/or palladium. Molybdenummay also be included in any of the formulations. For example, anotherembodiment may include substitution with palladium and molybdenum. Forexample, Example 122 may include 3 weight percent Mo. Another embodimentincluding molybdenum (and perhaps no manganese) may include 40 weightpercent cobalt, 18 weight percent chromium, 29 weight percent palladium,3 weight percent iron, and 10 weight percent nickel, as well as a traceamount (e.g., 0.1 weight percent) carbon. Such an embodiment may exhibita relative radiopacity of 6.3 barnes/cm³. Another embodiment may include53.4 weight percent cobalt, 20 weight percent chromium, 1.5 weightpercent manganese, 9.0 weight percent palladium, 1 weight percentplatinum, and 15 weight percent tungsten. An embodiment may include nonickel, which may be substituted with palladium, with platinum andmanganese, with palladium and manganese, or with palladium and iron.Substitution may be based on atomic, weight, or volume percentages of agiven component. An embodiment may maintain the Co/Cr ratio of thestarting alloy (e.g., L-605), and decrease the amounts of each (whilemaintaining the ratio), while increasing manganese content and/orincreasing platinum and/or palladium content. An embodiment may maintainthe Co/Cr ratio of the starting alloy, and add manganese with equalamounts (e.g., weight, volume, or atomic) of platinum and palladium,with tungsten. An embodiment may reduce the tungsten content (e.g., cutin half) and add molybdenum instead, while substituting nickel withplatinum and/or palladium. An embodiment may substitute iron for nickeland add palladium and/or platinum for partial cobalt replacement. Anembodiment may replace nickel with manganese and reduce cobalt by addingplatinum or palladium. An embodiment may maintain the Co/Cr ratio of thestarting alloy and add one or more of palladium, manganese, and/ormolybdenum.

In another embodiment, a radiopaque Co—Cr—Ni—W alloy is contemplatedthat is similar to L-605, but in which the amount of tungsten isincreased to 20-35% by weight, or up to 35% by weight, while theremaining weight fractions may remain unaltered. For example, alloyL-605 contains 15% by weight tungsten. By increasing the amount oftungsten to 20-35% by weight (by substituting some of the cobalt), whileretaining the remaining weight fractions, the relative radiopacity ofthe resulting alloy is increased relative to L-605, and where care istaken during manufacture to carefully quench the alloy, the resultingalloy can advantageously have a primarily single-phase, FCCmicrostructure. It will be appreciated that many other alloys that maynominally include such fractions of tungsten will not necessarilyinclude the required primarily single-phase FCC structure, but willinclude a coarse, Tungsten rich second phase (e.g. Co₃W due to theelevated Tungsten content) and/or a plurality of microcrystallinephases, due to the elevated tungsten content. At an elevated temperature(e.g., at about at least 1300° C., about at least 1400° C. or about atleast 1500° C.), a single-phase FCC structure can be achieved in suchCo—Cr alloys, and if care is taken in ensuring that cooling of the alloyoccurs quickly, with sufficient austenitic stabilization content (e.g.,Ni and Mn), it is possible to preserve a primarily single-phase alloy inwhich the tungsten (and the other alloying elements) continue toprimarily exhibit the FCC crystalline structure, rather than forming twocoarse phases, as would be typical.

The primarily single-phase alloy having an increased level of tungstenmay be attained by means of powder metallurgy processes, for example byforming a single-phase FCC alloy melt of the composition andsubsequently spraying the single-phase FCC alloy melt as quick coolingdroplets through a nozzle (e.g. droplets smaller than about 25 μm),pouring the single-phase FCC alloy melt against a spinning drum tocreate a fine ribbon or related techniques. The alloy melt must becompletely molten and may require superheat to counteract heat losses bythe feed system and the nozzle, such that the processes include heatingthe alloy melt to an elevated temperature of about at least 1300° C.,about at least 1400° C. or about at least 1500° C. prior to rapidcooling (e.g. 200 to 500° C./s). The resulting fine particles may have amaximum or even average particle size of 0.5 μm to 10 μm and form apowder which may then be compacted, sintered and optionally processed ina hot isostatic press to form a powder metallurgy billet analogous to acast ingot. The billet may then be processed in essentially the samemanner as a cast ingot.

Hot isostatic pressing subjects the powder to both an elevatedtemperature and isostatic gas pressure in a high-pressure containmentvessel, and may be adapted to achieve a minimum of 99.5% dense alloy.High sintering temperatures of about 1200 to 1300° C. may be used toenable high diffusion rates for promoting powder bonding and voidreduction. As the billets may be subsequently wrought into tubing orwire, additional densification may be achieved thereby. Age hardening ofthe alloy material may allow further optimization of the mechanicalproperties of the material, without a reduction in radiopacity orformation of a coarse second phase within the microstructure.

One embodiment of the radiopaque Co—Cr—Ni—W alloy of the presentinvention is comprised of chromium in a concentration of about 20%(e.g., 15% to 25%) by weight, tungsten in a concentration that isgreater than 15% (e.g., at least 20%, such as 20-35% by weight, nickelin a concentration of 5-15% (e.g., about 10%) by weight, manganese in aconcentration of 0-5% (e.g., 1-3%) by weight, and iron in aconcentration of 0-5% (e.g., 0-3%, or 1-3%) by weight. Trace elementsmay be present, if at all, in concentrations of less than 1%, less than0.5%, less than 0.4%, less than 0.3%, less than 0.2%, less than 0.1%,less than 0.05%, less than 0.04%, less than 0.03%, less than 0.02%, orless than 0.01% by weight. The balance of material is cobalt, e.g.,about 30-50% by weight. In an embodiment, the weight fractions for oneor more of chromium, manganese, iron, or nickel may be identical tothose in L-605. In an embodiment, the fractions of cobalt and tungstenmay be the only difference in composition relative to L-605, althoughthe sum of the cobalt+tungsten weight fractions may be equal to that ofL-605 (e.g., 66-68% by weight).

According to a further embodiment of the radiopaque Co—Cr—Ni—W alloy,the alloy may be substantially or entirely free of molybdenum and/orcarbon as deliberately added alloying elements. “Substantially free” asused herein may include less than 0.05%, less than 0.04%, less than0.03%, less than 0.02%, or less than 0.01% weight.

According to a further embodiment, the alloy comprises no more than 1%,no more than 0.5%, no more than 0.4%, no more than 0.3%, or no more than0.2% of silicon. The alloy may be substantially free of phosphorousand/or sulfur, as quantified above (e.g., no more than 0.02% by weightof each).

The radiopaque stent of the present invention overcomes limitations andweaknesses of other stents, e.g., particularly L-605 stents, whichexhibit less than optimal radiopacity, without requiring addition ofrelatively expensive alloying elements, such as platinum, palladium,iridium, or the like, while at the same time ensuring that the stent canbe formed from a homogenous material (no coatings, various metalliclayers, markers or the like), in which the alloy exhibits a primarilysingle-phase FCC microstructure, but with super-saturated tungstencontent. Such a stent imparts a more visible image when absorbing x-raysduring fluoroscopy as compared to a dimensionally similar L-605 stent,while providing other advantages over alternative stent alloys thatemploy expensive alloying elements. With this more visible image, theentire stent is better observed by the practitioner placing the stent.The image observed by the practitioner is not “washed out” due toexcessive brightness and is not too dim. Because of the improved image,the stent is accurately positioned and manipulated within a lumen of apatient, with a radiopacity such that stent expansion during and afterdeployment may be assessed accurately by the practitioner. An additionaladvantage to the increased radiopacity is the visualization of the stentand the underlying vessel during follow-up examinations by thepractitioner.

Because the entire stent is radiopaque, the diameter and length of thestent are readily discerned by the practitioner. Also, because the stentitself is made of the radiopaque alloy, the stent does not have problemsassociated with radiopaque coatings or varying metallic layers, such ascracking or separation or corrosion. Also, because the entire stent isradiopaque, the stent does not require extra markers with theirattendant issues.

The low profile of the Co—Cr—Ni—W stent, coupled with its enhancedradiopacity renders the stent more deliverable with easier observationand detection throughout its therapeutic use than stents heretoforeavailable, at a lower cost. A stent constructed of a Co—Cr—Ni—W alloy ascontemplated herein can be made thinner than one of stainless steelwithout sacrificing fluoroscopic visibility and can be free from costlyplatinum group metals, precious metals, and other relatively expensiveexotic metals. The low profile of the Co—Cr—Ni—W stent renders the stentmore deliverable with greater flexibility.

Furthermore, the use of a Co—Cr—Ni—W alloy that includes up to 35% byweight tungsten, or particularly 20-35% tungsten, in a primarilysingle-phase composition results in improved radiopacity of the lowprofile stent of the present invention over prior art cobalt chromiumalloys using lesser amounts of tungsten as a radiopacifier, andincreases deliverability of the stent and offers solid performanceadvantages regarding decreasing the fluid mechanical disturbances ofblood flow. Improved radiopacity assists the practitioner in placing thedevice precisely. Inflation or other deployment of the stent is bettermonitored because the stent is better visible to the practitioner. Thisvisibility reduces the incidence and probability of an under-deployedstent. Further, in-stent restenosis is monitored as the stent and aninjected contrast agent are able to be imaged simultaneously. Unlikesome stents, the stent of the present invention does not produce animage which is too bright, thereby obscuring imaging of the underlyingvessel morphology.

The use of tungsten may not only impart an improved radiopacity but alsoimpart improved corrosion resistance and a resistance to oxidation athigh temperatures.

While cobalt chromium alloys containing up to 15% by weight tungsten,such as L-605, have been used in many applications, these alloys areunable to replicate the improved radiopacity achieved with platinumgroup metals and other precious metals known in the art. The nominalcomposition of L-605 is shown in Table 1.

L-605 is reported to have a melting range of 1602 to 1683K (e.g., 1329to 1410° C.) a maximum hardness of 277 HB and a density of 9.13 g/cm³.This alloy in annealed bar form has a minimum ultimate tensile strengthof 125 ksi, a minimum yield strength of 45 ksi and a minimum totalelongation of 30%. While many of these properties are desirable, andsuitable for stent manufacture, the relative radiopacity of L-605 islacking, e.g., being only 3.6 barnes/cc. While this is better thanstainless steel (with a relative radiopacity of only about 2.5barnes/cc), it is far below a more suitable range, such as greater than4 barnes/cc, greater than 4.5 barnes/cc, or from 4 barnes/cc to 10barnes/cc, 4 barnes/cc to 8 barnes/cc, or 4 barnes/cc to 7 barnes/cc.

Variations in the level of tungsten in the cobalt chromium alloy L-605,and by extension in the radiopacity of the alloy, have previously beenrestricted to 15% by weight, due to the solubility limits of tungsten insuch Co—Cr alloys, as well as other restraints. As shown in FIGS.61a-62c , attempts to increase tungsten past the solubility limit,according to known methods in the prior art, results in multiple coarsephases (rather than primarily a single FCC phase with a finelydistributed second phase) leading to loss of desirable mechanicalproperties of the L-605 microstructure and alloy. According to FIGS.61a-c , an increased tungsten content of 20% leads to an unacceptablylarge second phase of Co₃W that is concentrated in the material. At alevel of 25% tungsten the second phase becomes even more pervasive, asillustrated in a comparison of FIGS. 61a-c with FIGS. 62a-c . The lossof a primarily single-phase austenitic microstructure in an alloy withsupersaturated levels of tungsten impairs the mechanical properties ofthe alloy and can cause material weaknesses, e.g. due to the stressconcentrations caused by the presence of the coarse second phaseparticles. These large particles are further subject to selective attackduring processing and should be avoided.

It has not previously been possible to increase the level of tungsten inthe alloy to 20-35% without losing the advantages of a single-phaseaustenitic microstructure, or at least a primarily single-phaseaustenitic microstructure. This is due at least in part to the lowsolubility limit of tungsten within the alloy at usage temperatures, andthe tendency for increased levels of tungsten in the alloy to induce theformation of a coarse multiphase microstructure. This coarse multiphasemicrostructure is subject to selective attack, and exhibits decreasedmechanical properties. Tungsten is actually a HCP stabilizer, not an FCCstabilizer and is known to form coarse phases of Co₃W and Co₇W₆.

While some attempts have been made to improve the radiopacity of L-605,these strategies have generally relied on the replacement of nickelwithin the alloy, and require the use of expensive and exotic elements.Even where such may increase radiopacity, they can result in a decreasein other desirable mechanical properties, and may not result a primarilysingle-phase microstructure, particularly where the austeniticstabilizer nickel is removed. Further, the inherent expense may be costprohibitive in a competitive business environment.

Materials having a coarse multiphase microstructure are prone to defectsin processing and are disadvantageous for use in stent products. Ofparticular concern is the tendency of high levels of tungsten to causesegregation in the initial as cast material. During heat treatment caremust be taken for complete homogeneity. Appropriate processes formaintaining a high homogeneity in the alloy requires the use of hightemperatures in the solution and rapid cooling by quenching or usingpowder metallurgy processes.

The currently described embodiments having 20-35% tungsten have beenfound to improve the radiopacity of the material to comparable levelsachieved by alloys relying on platinum group metals or other exoticmetals addition, but without compromising the primarily single-phase,FCC microstructure that is one advantage of an otherwise inferior L-605alloy. In addition, tungsten is relatively abundant and inexpensive ascompared to many alternative proposed radiopacity increasing alloyingmetals.

To form a Co—Cr—Ni—W alloy having 20-35% tungsten according to oneembodiment of the present disclosure, each of the principal elements(i.e., cobalt, chromium, nickel and tungsten) can be refined to form afurnace charge stock that is combined in an alloy melt and cast asingots. The refined principal elements are combined in solution at ahigh temperature of at least about 1500K, (e.g., 1227° C.), under whichconditions the solubility limit of tungsten in the solution is increasedsignificantly, and to achieve homogenization of the elements in aprimarily single-phase FCC microstructure. FIGS. 58-60 show how suchCo—Cr—Ni—W alloys exhibit greater equilibrium solubility of the tungstenat elevated temperatures (e.g., at about 1500K), and that thisequilibrium solubility drops significantly at 500K (and it is similarlylow at ambient temperature (e.g., 293K). FIGS. 55-57 show simple binaryphase diagrams from Co—W, Cr—W, and Ni—W, respectively. In order toachieve good homogenization of the elements at the elevated temperature(e.g., at least about 1500K), the process may include maintaining thesolid solution at said temperature for a given period of time in orderto ensure the desired uniform homogenous distribution of tungsten andthe other alloying elements throughout the solution. For example, thesolution may be maintained at said temperature for at least about 1minute, at least about 2 minutes, at least about 3 minutes, at leastabout 5 minutes, from 1 minute to 200 minutes, from 1 minute to 100minutes, from 1 minute to about 60 minutes, or from 1 to 30 minutes.Such a dwell time at the elevated temperature also ensures that thesolution has sufficient time to reach the equilibrium state in which thesingle-phase FCC structure is attained. The solution is cooled from therelatively high processing temperature to about 500K or less (e.g., 227°C.), within a short time period (e.g., less than 10 minutes, less than 5minutes, less than 4 minutes, less than 3 minutes, less than 2 minutes,or less than 1 minute), in order to keep high levels of tungsten trappedin solution with a primarily single-phase FCC microstructure, and toprevent the tungsten from precipitating out of the single-phase alloy,which would result in formation of a second phase of uncontrolled size.Rapid cooling of the solution may thus maintain the supersaturatedcomposition with regards to tungsten in the alloy.

According to one embodiment of the disclosure, an alloy melt of theCo—Cr—Ni—W alloy having 20-35% tungsten may undergo rapid coolingaccording to powder metallurgy processes or ribbon cooling. In a powdermetallurgy process, the alloy melt may be forced through a nozzle forforming fine droplets that can be cooled within a shorter time periodthan that achievable by quenching. In an example, the nozzle may beadapted for forming droplets smaller than 25 μm. A resulting powderincluding a primarily single-phase alloy according to the disclosure maythen be processed by compaction, sintering and optionally isostaticpressing to form an alloy billet. The alloy billet may then be processedin a manner analogous to an as cast ingot.

Hot isostatic pressing subjects the powder to both an elevatedtemperature and isostatic gas pressure in a high-pressure containmentvessel, and may be adapted to achieve a minimum of 99.5% dense alloy.High sintering temperatures of about 1200 to 1300° C. may be used toenable high diffusion rates for promoting powder bonding and voidreduction. As the billets may be subsequently wrought into tubing orwire, additional densification may be achieved thereby.

In ribbon cooling the alloy melt may be poured against a drum spinningat a high speed. A resulting fine ribbon has a small size, that issubjected to a higher rate of cooling than is possible using quenchingtechniques, such that the formation of a second phase is limited in theresulting alloy.

Advantageously, the nickel, and optionally manganese, of the Co—Cr—Ni—Walloy serve as austenitic stabilizers within the solution and aid inpreserving the desired primarily single-phase, FCC microstructure duringthe rapid cooling step, despite the amount of tungsten being above itssolubility limit at room temperature. For this reason, it can beimportant in such embodiments where a primarily single-phase FCCmicrostructure is desired, to not substitute any of the 10% by weightnickel content already present in a comparative L-605 alloy. Forexample, nickel suppresses cobalt's allotropic transformation from aface-centered-cubic (“FCC”) crystal structure (where it is stable athigh temperatures) to a hexagonal-close-packed (“HCP”) structure (whereit is stable at low temperatures). These characteristics are apparentfrom FIGS. 11-16. In pure cobalt, this transformation naturally occursat around 422° C. The addition of nickel significantly reduces cobalt'stransformation temperature, thereby favoring the FCC structure, which ingeneral, is a more ductile and more creep-resistant crystal structurethan HCP. The rapid cooling of the alloy solution serves to trap thetungsten in the favored FCC structure, minimizing or eliminatingformation of any substantial amounts of HCP or other structural phases.

While existing processing methods for L-605 generally adapt sometemperature considerations to balance control of carbide formation inthe alloy material with the desired mechanical properties of the finalmaterial, up to now, no consideration has been given to the processingthat would be required to maintain a primarily single-phase, FCCmicrostructure in a Co—Cr—Ni—W alloy with 20-35 weight percent tungsten,paired with other compositional characteristics as shown in Examples133-136. As some embodiments of the current Co—Cr—Ni—W alloys may beentirely free of carbon, the temperatures and cooling times of theprocessing described herein may be directly focused on the incorporationand homogenization of tungsten into the alloy solution with a primarilysingle-phase, FCC microstructure, rather than any considerations relatedto carbide formation.

By so processing the alloy, it is expected that it is possible toincorporate tungsten in the Co—Cr—Ni—W alloy material at 20-35% byweight (far above its room temperature solubility limit) while retainingthe critical feature of a primarily single-phase FCC microstructure. Theincreased level of tungsten increases the radiopacity of the alloymaterial without the need for platinum group metals or other precious orexpensive, exotic metals. According to one embodiment, the Co—Cr—Ni—Walloy is completely free of platinum group metals, precious metals, orother expensive elements such as platinum, palladium, ruthenium,rhodium, osmium, iridium, hafnium, rhenium, tantalum, niobium,molybdenum, zirconium, silver, gold or combinations thereof. While ironand/or manganese may be present, they each may represent no more than3%, or no more than 2% (e.g., 1.5% by weight) of the alloy. The alloymay also be free, or substantially free of other elements of theperiodic table not specifically listed in Examples 133-136.

The resulting alloys are advantageously stable and capable of additionalhomogenization and refining, such as age hardening, without a loss ofradiopacity or the benefits of a primarily single-phase microstructure.In order to achieve the advantages of a very fine second phase from agehardening, the process may include an additional heating step followingthe rapid cooling or quenching of the primarily single-phase solution.For example, the resultant primarily single-phase FCC material may beheated at 600 to 1000° C., 600 to 800° C., or 600 to 675° C. for atleast about 1 hour, at least about 4 hours, at least about 8 hours, atleast about 16 hours, from 1 hour to 256 hours, or from 1 hour to 16hours. Aging for the described time periods at the describedtemperatures ensures that the material has sufficient time to form avery fine second phase of fine particulate Co₃W. The austeniticstabilization of the material advantageously prevents significantformation of HCP structure, which would result in formation of multiplephases, while allowing the formation of fine particulate Co₃W whichimpedes the movement of dislocations or defects within themicrostructure of the material. The age hardening can be configured toimpart a particular yield strength to the material, according to theenvisioned use, without causing any tangible effect on the advantageousradiopacity and mechanical properties of the single-phase supersaturatedtungsten alloy.

Known methods for processing L605 alloys generally do not employ powdermetallurgy or age hardening, as there was no apparent perceivedcommercial advantage in doing so. Prior to the discoveries of thecurrent disclosure, powder metallurgy was perceived as a costly methodthat provided insufficient benefit in material properties. However,according to the current disclosure, powder metallurgy methods forforming an L605 alloy having increased levels of tungsten can reduce theoccurrence of a disadvantageous second phase, such that the second phaseis limited to no more than 10% volume fraction of a second phase,preferably no more than 5% volume fraction of a second phase. Theresultant second phase further has a maximum or even average particlesize of 0.5 μm to 5 μm and improves the yield strength of the material.In one embodiment, the alloy of the current disclosure may have a yieldstrength of 45 KSi or 310 MPa.

For some embodiments, the components of the Co—Cr—Ni—W alloy may becombined in an alloy melt by vacuum induction melting. Final refiningmay be performed in a vacuum arc remelt furnace. Homogenization may beperformed to eliminate segregation, while the cooling step may includequenching the alloy solution with water, another liquid (e.g., oil)and/or a suitable gas, or cooling through powder metallurgy methods orribbon cooling.

Experimental results illustrate the possibility of creating a radiopaqueCo—Cr—Ni—W alloy having 20-35% tungsten by weight, as shown by Examples133-136 below.

Example 133

Atomic Atomic # Symbol Name Wt Weight % Atomic % 1 H Hydrogen 1.007940.00 0.00 5 B Boron 10.811 0.00 0.00 6 C Carbon 12.0107 0.00 0.00 7 NNitrogen 14.0067 0.00 0.00 8 O Oxygen 15.9994 0.00 0.00 14 Si Silicon28.0855 0.20 0.47 15 P Phosphorous 30.97376 0.02 0.04 16 Si Sulfur32.065 0.02 0.03 24 Cr Chromium 51.9961 20.00 25.31 25 Mn Manganese54.93805 1.50 1.80 26 Fe Iron 55.845 1.50 1.77 27 Co Cobalt 58.933246.76 52.21 28 Ni Nickel 58.6934 10.00 11.21 74 W Tungsten 183.84 20.007.16 77 Ir Iridium 192.217 0.00 0.00 78 Pt Platinum 195.084 0.00 0.00103 Lr Lawrencium 262 0.00 0.00 Total 100.00 100.00 W/Co 0.43 0.14

Example 134

Atomic Atomic # Symbol Name Wt Weight % Atomic % 1 H Hydrogen 1.007940.00 0.00 5 B Boron 10.811 0.00 0.00 6 C Carbon 12.0107 0.00 0.00 7 NNitrogen 14.0067 0.00 0.00 8 O Oxygen 15.9994 0.00 0.00 14 Si Silicon28.0855 0.20 0.47 15 P Phosphorous 30.97376 0.02 0.04 16 Si Sulfur32.065 0.02 0.03 24 Cr Chromium 51.9961 20.00 25.31 25 Mn Manganese54.93805 1.50 1.80 26 Fe Iron 55.845 1.50 1.77 27 Co Cobalt 58.933241.76 48.47 28 Ni Nickel 58.6934 10.00 11.21 74 W Tungsten 183.84 25.009.30 77 Ir Iridium 192.217 0.00 0.00 78 Pt Platinum 195.084 0.00 0.00103 Lr Lawrencium 262 0.00 0.00 Total 100.00 100.00 W/Co 0.60 0.19

Example 135

Atomic Atomic # Symbol Name Wt Weight % Atomic % 1 H Hydrogen 1.007940.00 0.00 5 B Boron 10.811 0.00 0.00 6 C Carbon 12.0107 0.00 0.00 7 NNitrogen 14.0067 0.00 0.00 8 O Oxygen 15.9994 0.00 0.00 14 Si Silicon28.0855 0.20 0.47 15 P Phosphorous 30.97376 0.02 0.04 16 Si Sulfur32.065 0.02 0.03 24 Cr Chromium 51.9961 20.00 25.31 25 Mn Manganese54.93805 1.50 1.80 26 Fe Iron 55.845 1.50 1.77 27 Co Cobalt 58.933236.76 44.42 28 Ni Nickel 58.6934 10.00 11.21 74 W Tungsten 183.84 30.0011.62 77 Ir Iridium 192.217 0.00 0.00 78 Pt Platinum 195.084 0.00 0.00103 Lr Lawrencium 262 0.00 0.00 Total 100.00 100.00 W/Co 0.82 0.26

Example 136

Atomic Atomic # Symbol Name Wt Weight % Atomic % 1 H Hydrogen 1.007940.00 0.00 5 B Boron 10.811 0.00 0.00 6 C Carbon 12.0107 0.00 0.00 7 NNitrogen 14.0067 0.00 0.00 8 O Oxygen 15.9994 0.00 0.00 14 Si Silicon28.0855 0.20 0.47 15 P Phosphorous 30.97376 0.02 0.04 16 Si Sulfur32.065 0.02 0.03 24 Cr Chromium 51.9961 20.00 25.31 25 Mn Manganese54.93805 1.50 1.80 26 Fe Iron 55.845 1.50 1.77 27 Co Cobalt 58.933231.76 40.02 28 Ni Nickel 58.6934 10.00 11.21 74 W Tungsten 183.84 35.0014.14 77 Ir Iridium 192.217 0.00 0.00 78 Pt Platinum 195.084 0.00 0.00103 Lr Lawrencium 262 0.00 0.00 Total 100.00 100.00 W/Co 1.10 0.35

Although described principally for use in manufacturing stents, it willbe understood that any of the disclosed alloys may also be used in themanufacture of guide wires, guide wire tip coils, balloon markers, orother structures associated with catheter use, and other implantablestructures in which improved radiopacity would be desirable.

The present invention can be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. Thus, thedescribed implementations are to be considered in all respects only asillustrative and not restrictive. The scope of the invention is,therefore, indicated by the appended claims rather than by the foregoingdescription. All changes that come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

The invention claimed is:
 1. A radiopaque stent, comprising: acylindrical main body comprising a cobalt-chromium alloy includingcobalt and chromium, the cobalt-chromium alloy including tungsten as aradiopacity increasing element, the tungsten comprising about 20% toabout 35% by weight of the cobalt-chromium alloy, the tungsten contentbeing super-saturated, above the solubility limit of tungsten in thecobalt-chromium alloy; wherein the cobalt-chromium alloy furthercomprises nickel, the nickel being present in a concentration of 5% toabout 15% by weight; and wherein the cobalt-chromium alloy exhibits aprimarily single-phase FCC solid solution, wherein a second phase of thetungsten is present and makes up no more than 10% volume fraction in thecobalt-chromium alloy, the second phase having an average particle sizeof less than 5 μm, even with the super-saturated tungsten content. 2.The radiopaque stent of claim 1, wherein the cobalt-chromium alloycomprises cobalt in an amount from about 30% to about 50% by weight ofthe cobalt-chromium alloy.
 3. The radiopaque stent of claim 1, whereinthe cobalt-chromium alloy comprises chromium in an amount of about 20%by weight of the cobalt-chromium alloy.
 4. The radiopaque stent of claim1, wherein the cobalt-chromium alloy comprises nickel in an amount ofabout 10% by weight of the cobalt-chromium alloy.
 5. The radiopaquestent of claim 1, wherein the cobalt-chromium alloy is entirely free ofmolybdenum.
 6. The radiopaque stent of claim 1, wherein thecobalt-chromium alloy comprises no more than 1% of silicon, phosphorus,and/or sulfur by weight.
 7. The radiopaque stent of claim 1, wherein thecobalt-chromium alloy further comprises manganese in a concentration ofup to 5% by weight of the cobalt-chromium alloy.
 8. The radiopaque stentof claim 1, wherein the cobalt-chromium alloy further comprises iron ina concentration of up to 5% by weight of the cobalt-chromium alloy. 9.The radiopaque stent of claim 1, wherein the cobalt-chromium alloyfurther comprises both manganese and iron in a concentration of about1.5% each, by weight.
 10. The radiopaque stent of claim 1, whereincobalt comprises from about 66 to 68% by weight of the cobalt-chromiumalloy.
 11. The radiopaque stent of claim 1, wherein a weight percentratio of tungsten to cobalt is at least 0.4.
 12. The radiopaque stent ofclaim 1, wherein a ratio of tungsten to cobalt is from 0.4 to 1.2. 13.The radiopaque stent of claim 1, wherein a ratio of tungsten to cobaltis from 0.40 to 0.45.
 14. The radiopaque stent of claim 1, wherein aratio of tungsten to cobalt is from 0.57 to 0.63.
 15. The radiopaquestent of claim 1, wherein a ratio of tungsten to cobalt is from 1.07 to1.13.
 16. The radiopaque stent of claim 1, wherein the cobalt-chromiumalloy is substantially free of carbon.
 17. A radiopaque stent,comprising: a cylindrical main body formed from a single homogenouscobalt-chromium alloy including cobalt, chromium, nickel, and tungsten,the cobalt-chromium alloy not including any other alloying elements inamounts greater than 3% by weight; the cobalt-chromium alloy includingtungsten as a radiopacity increasing element, the tungsten comprisingabout 20% to about 35% by weight of the cobalt-chromium alloy, thetungsten content being super-saturated, above the solubility limit oftungsten in the cobalt-chromium alloy at ambient temperature; whereinthe cobalt-chromium alloy comprises about 10% by weight nickel; andwherein the cobalt-chromium alloy exhibits a primarily single-phase FCCsolid solution structure, a second phase of the tungsten is present inthe cobalt-chromium alloy having a maximum particle size of less than 15μm, even with the super-saturated tungsten content.
 18. The radiopaquestent of claim 17, wherein the cobalt-chromium alloy is entirely free ofmolybdenum.
 19. The radiopaque stent of claim 17, wherein thecobalt-chromium alloy is substantially free of carbon.
 20. Theradiopaque stent of claim 17, wherein the cobalt-chromium alloy isentirely free of carbon.
 21. A radiopaque stent, comprising: acylindrical main body comprising a cobalt-chromium alloy includingcobalt and chromium, the cobalt-chromium alloy including tungsten as aradiopacity increasing element, the tungsten comprising about 20% toabout 35% by weight of the cobalt-chromium alloy, the tungsten contentbeing super-saturated, above the solubility limit of tungsten in thecobalt-chromium alloy; wherein the cobalt-chromium alloy furthercomprises nickel, the nickel being present in a concentration of 5% toabout 15% by weight; wherein the cobalt-chromium alloy exhibits aprimarily single-phase FCC solid solution, wherein no more than 10%volume fraction of a second phase of the tungsten is present in thecobalt-chromium alloy, the second phase having an average particle sizeof less than 5 μm, even with the super-saturated tungsten content; andat least one of (i) or (ii): (i) wherein a ratio of tungsten to cobaltis from 1.07 to 1.13; (ii) wherein the cobalt-chromium alloy furthercomprises both manganese and iron in a concentration of about 1.5% each,by weight.
 22. The radiopaque stent of claim 1, wherein the tungstencomprises 25% to about 30% by weight of the cobalt-chromium alloy.